Index: generic/gentclAPI.tcl
===================================================================
diff -u -rb8af431b779825e6d2cfa7a8b334158da1ea9370 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/gentclAPI.tcl	(.../gentclAPI.tcl)	(revision b8af431b779825e6d2cfa7a8b334158da1ea9370)
+++ generic/gentclAPI.tcl	(.../gentclAPI.tcl)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -89,14 +89,14 @@
       set if [list "XOTclClass *cl"]
       append intro \
           "  XOTclClass *cl =  XOTclObjectToClass(clientData);" \n \
-          {  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");}
+          {  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");}
     }
     object {
       set a  [list obj]
       set if [list "XOTclObject *obj"]
       append intro \
           "  XOTclObject *obj =  (XOTclObject *)clientData;" \n \
-          {  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");}
+          {  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");}
     }
     ""    {
       set a [list]
Index: generic/predefined.h
===================================================================
diff -u -r464811a4aaa475de10e834b0a009521446163fc0 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/predefined.h	(.../predefined.h)	(revision 464811a4aaa475de10e834b0a009521446163fc0)
+++ generic/predefined.h	(.../predefined.h)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -440,15 +440,16 @@
 "proc createBootstrapAttributeSlots {} {}\n"
 "::xotcl::Slot method type=hasmixin {name value arg} {\n"
 "if {![::xotcl::is $value hasmixin $arg]} {\n"
-"error \"Value '$value' of $name has not mixin $arg\"}\n"
+"error \"Value '$value' of $name has not mixin $arg\"\n"
+"error \"expected object with mixin $arg but got \\\"$value\\\" for parameter $name\"}\n"
 "return $value}\n"
 "::xotcl::Slot method type=baseclass {name value} {\n"
 "if {![::xotcl::is $value baseclass]} {\n"
-"error \"Value '$value' of $name is not a baseclass\"}\n"
+"error \"expected baseclass but got \\\"$value\\\" for parameter $name\"}\n"
 "return $value}\n"
 "::xotcl::Slot method type=metaclass {name value} {\n"
 "if {![::xotcl::is $value metaclass]} {\n"
-"error \"Value '$value' of $name is not a metaclass\"}\n"
+"error \"expected metaclass but got \\\"$value\\\" for parameter $name\"}\n"
 "return $value}}\n"
 "::xotcl2::Class create ::xotcl::ScopedNew -superclass ::xotcl2::Class -parameter {\n"
 "{withclass ::xotcl2::Object}\n"
Index: generic/predefined.xotcl
===================================================================
diff -u -ra38906707b8e508b97f01c9b68071c927c2a5d0f -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/predefined.xotcl	(.../predefined.xotcl)	(revision a38906707b8e508b97f01c9b68071c927c2a5d0f)
+++ generic/predefined.xotcl	(.../predefined.xotcl)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -850,18 +850,19 @@
   ::xotcl::Slot method type=hasmixin {name value arg} {
     if {![::xotcl::is $value hasmixin $arg]} {
       error "Value '$value' of $name has not mixin $arg"
+      error "expected object with mixin $arg but got \"$value\" for parameter $name"
     }
     return $value
   }
   ::xotcl::Slot method type=baseclass {name value} {
     if {![::xotcl::is $value baseclass]} {
-      error "Value '$value' of $name is not a baseclass"
+      error "expected baseclass but got \"$value\" for parameter $name"
     }
     return $value
   }
   ::xotcl::Slot method type=metaclass {name value} {
     if {![::xotcl::is $value metaclass]} {
-      error "Value '$value' of $name is not a metaclass"
+      error "expected metaclass but got \"$value\" for parameter $name"
     }
     return $value
   }
Index: generic/tclAPI.h
===================================================================
diff -u -r464811a4aaa475de10e834b0a009521446163fc0 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/tclAPI.h	(.../tclAPI.h)	(revision 464811a4aaa475de10e834b0a009521446163fc0)
+++ generic/tclAPI.h	(.../tclAPI.h)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -373,7 +373,7 @@
 XOTclCAllocMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCAllocMethodIdx].paramDefs, 
                      method_definitions[XOTclCAllocMethodIdx].nrParameters, 
@@ -392,7 +392,7 @@
 XOTclCCreateMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCCreateMethodIdx].paramDefs, 
                      method_definitions[XOTclCCreateMethodIdx].nrParameters, 
@@ -411,7 +411,7 @@
 XOTclCDeallocMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCDeallocMethodIdx].paramDefs, 
                      method_definitions[XOTclCDeallocMethodIdx].nrParameters, 
@@ -430,7 +430,7 @@
 XOTclCFilterGuardMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCFilterGuardMethodIdx].paramDefs, 
                      method_definitions[XOTclCFilterGuardMethodIdx].nrParameters, 
@@ -450,7 +450,7 @@
 XOTclCInvalidateObjectParameterMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCInvalidateObjectParameterMethodIdx].paramDefs, 
                      method_definitions[XOTclCInvalidateObjectParameterMethodIdx].nrParameters, 
@@ -469,7 +469,7 @@
 XOTclCMixinGuardMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCMixinGuardMethodIdx].paramDefs, 
                      method_definitions[XOTclCMixinGuardMethodIdx].nrParameters, 
@@ -489,7 +489,7 @@
 XOTclCNewMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCNewMethodIdx].paramDefs, 
                      method_definitions[XOTclCNewMethodIdx].nrParameters, 
@@ -508,7 +508,7 @@
 XOTclCRecreateMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclClass *cl =  XOTclObjectToClass(clientData);
-  if (!cl) return XOTclObjErrType(interp, objv[0], "Class");
+  if (!cl) return XOTclObjErrType(interp, objv[0], "Class", "");
   if (ArgumentParse(interp, objc, objv, (XOTclObject *) cl, objv[0], 
                      method_definitions[XOTclCRecreateMethodIdx].paramDefs, 
                      method_definitions[XOTclCRecreateMethodIdx].nrParameters, 
@@ -1207,7 +1207,7 @@
 XOTclOAutonameMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOAutonameMethodIdx].paramDefs, 
                      method_definitions[XOTclOAutonameMethodIdx].nrParameters, 
@@ -1228,7 +1228,7 @@
 XOTclOCleanupMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOCleanupMethodIdx].paramDefs, 
                      method_definitions[XOTclOCleanupMethodIdx].nrParameters, 
@@ -1246,7 +1246,7 @@
 static int
 XOTclOConfigureMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
     
 
     return XOTclOConfigureMethod(interp, obj, objc, objv);
@@ -1257,7 +1257,7 @@
 XOTclODestroyMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclODestroyMethodIdx].paramDefs, 
                      method_definitions[XOTclODestroyMethodIdx].nrParameters, 
@@ -1276,7 +1276,7 @@
 XOTclOExistsMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOExistsMethodIdx].paramDefs, 
                      method_definitions[XOTclOExistsMethodIdx].nrParameters, 
@@ -1295,7 +1295,7 @@
 XOTclOFilterGuardMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOFilterGuardMethodIdx].paramDefs, 
                      method_definitions[XOTclOFilterGuardMethodIdx].nrParameters, 
@@ -1315,7 +1315,7 @@
 XOTclOFilterSearchMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOFilterSearchMethodIdx].paramDefs, 
                      method_definitions[XOTclOFilterSearchMethodIdx].nrParameters, 
@@ -1333,7 +1333,7 @@
 static int
 XOTclOInstVarMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
     
 
     return XOTclOInstVarMethod(interp, obj, objc, objv);
@@ -1344,7 +1344,7 @@
 XOTclOMixinGuardMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOMixinGuardMethodIdx].paramDefs, 
                      method_definitions[XOTclOMixinGuardMethodIdx].nrParameters, 
@@ -1363,7 +1363,7 @@
 static int
 XOTclONextMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
     
 
     return XOTclONextMethod(interp, obj, objc, objv);
@@ -1374,7 +1374,7 @@
 XOTclONoinitMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclONoinitMethodIdx].paramDefs, 
                      method_definitions[XOTclONoinitMethodIdx].nrParameters, 
@@ -1393,7 +1393,7 @@
 XOTclORequireNamespaceMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclORequireNamespaceMethodIdx].paramDefs, 
                      method_definitions[XOTclORequireNamespaceMethodIdx].nrParameters, 
@@ -1411,7 +1411,7 @@
 static int
 XOTclOResidualargsMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
     
 
     return XOTclOResidualargsMethod(interp, obj, objc, objv);
@@ -1421,7 +1421,7 @@
 static int
 XOTclOUplevelMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
     
 
     return XOTclOUplevelMethod(interp, obj, objc, objv);
@@ -1431,7 +1431,7 @@
 static int
 XOTclOUpvarMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
     
 
     return XOTclOUpvarMethod(interp, obj, objc, objv);
@@ -1442,7 +1442,7 @@
 XOTclOVolatileMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOVolatileMethodIdx].paramDefs, 
                      method_definitions[XOTclOVolatileMethodIdx].nrParameters, 
@@ -1461,7 +1461,7 @@
 XOTclOVwaitMethodStub(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   parseContext pc;
   XOTclObject *obj =  (XOTclObject *)clientData;
-  if (!obj) return XOTclObjErrType(interp, objv[0], "Object");
+  if (!obj) return XOTclObjErrType(interp, objv[0], "Object", "");
   if (ArgumentParse(interp, objc, objv, obj, objv[0], 
                      method_definitions[XOTclOVwaitMethodIdx].paramDefs, 
                      method_definitions[XOTclOVwaitMethodIdx].nrParameters, 
Index: generic/xotcl.c
===================================================================
diff -u -r464811a4aaa475de10e834b0a009521446163fc0 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/xotcl.c	(.../xotcl.c)	(revision 464811a4aaa475de10e834b0a009521446163fc0)
+++ generic/xotcl.c	(.../xotcl.c)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -6214,7 +6214,8 @@
 	*outObjPtr = objPtr;
       } else {
 	result = XOTclVarErrMsg(interp, "expected ", ObjStr(pPtr->converterArg), 
-				" but got \"", ObjStr(objPtr), "\"", NULL);
+				" but got \"", ObjStr(objPtr), 
+                                "\" for parameter ", pPtr->name, NULL);
       }
     }
   } else {
@@ -6235,17 +6236,27 @@
 			    ClientData *clientData, Tcl_Obj **outObjPtr) {
   int result, bool;
   result = Tcl_GetBooleanFromObj(interp, objPtr, &bool);
-  if (result == TCL_OK) *clientData = (ClientData)INT2PTR(bool);
-  *outObjPtr = objPtr;
+  if (result == TCL_OK) {
+    *clientData = (ClientData)INT2PTR(bool);
+    *outObjPtr = objPtr;
+  } else {
+    XOTclVarErrMsg(interp, "expected boolean value but got \"", ObjStr(objPtr), 
+                   "\" for parameter ", pPtr->name, NULL);
+  }
   return result;
 }
 
 static int convertToInteger(Tcl_Interp *interp, Tcl_Obj *objPtr,  XOTclParam CONST *pPtr, 
 			    ClientData *clientData, Tcl_Obj **outObjPtr) {
   int result, i;
   result = Tcl_GetIntFromObj(interp, objPtr, &i);
-  if (result == TCL_OK) *clientData = (ClientData)INT2PTR(i);
-  *outObjPtr = objPtr;
+  if (result == TCL_OK) {
+    *clientData = (ClientData)INT2PTR(i);
+    *outObjPtr = objPtr;
+  } else {
+    XOTclVarErrMsg(interp, "expected integer but got \"", ObjStr(objPtr), 
+                   "\" for parameter ", pPtr->name, NULL);
+  }
   return result;
 }
 
@@ -6271,7 +6282,7 @@
   Tcl_DStringAppend(dsPtr, what, -1);
   Tcl_DStringAppend(dsPtr, " of type ", -1);
   Tcl_DStringAppend(dsPtr, ObjStr(pPtr->converterArg), -1);
-  XOTclObjErrType(interp, objPtr, Tcl_DStringValue(dsPtr));
+  XOTclObjErrType(interp, objPtr, Tcl_DStringValue(dsPtr), pPtr->name);
   DSTRING_FREE(dsPtr);
 
   return TCL_ERROR;
@@ -6283,7 +6294,7 @@
   if (GetObjectFromObj(interp, objPtr, (XOTclObject **)clientData) == TCL_OK) {
     return objectOfType(interp, (XOTclObject *)*clientData, "object", objPtr, pPtr);
   }
-  return XOTclObjErrType(interp, objPtr, "object");
+  return XOTclObjErrType(interp, objPtr, "object", pPtr->name);
 }
 
 static int convertToClass(Tcl_Interp *interp, Tcl_Obj *objPtr,  XOTclParam CONST *pPtr, 
@@ -6292,7 +6303,7 @@
   if (GetClassFromObj(interp, objPtr, (XOTclClass **)clientData, 0) == TCL_OK) {
     return objectOfType(interp, (XOTclObject *)*clientData, "class", objPtr, pPtr);
   }
-  return XOTclObjErrType(interp, objPtr, "class");
+  return XOTclObjErrType(interp, objPtr, "class", pPtr->name);
 }
 
 static int convertToRelation(Tcl_Interp *interp, Tcl_Obj *objPtr,  XOTclParam CONST *pPtr, 
@@ -8806,7 +8817,7 @@
 XOTclSetterMethod(ClientData clientData, Tcl_Interp *interp, int objc, Tcl_Obj *CONST objv[]) {
   XOTclObject *object = (XOTclObject*)clientData;
 
-  if (!object) return XOTclObjErrType(interp, objv[0], "object");
+  if (!object) return XOTclObjErrType(interp, objv[0], "object", ObjStr(objv[0]));
   if (objc > 2) return XOTclObjErrArgCnt(interp, object->cmdName, objv[0], "?value?");
   return setInstVar(interp, object, objv[0], objc == 2 ? objv[1] : NULL);
 }
@@ -9079,7 +9090,7 @@
   */
 #endif
 
-  if (!tcd || !tcd->obj) return XOTclObjErrType(interp, objv[0], "object");
+  if (!tcd || !tcd->obj) return XOTclObjErrType(interp, objv[0], "object", "");
 
   if (tcd->passthrough) { /* two short cuts for simple cases */
     /* early binding, cmd *resolved, we have to care only for objscope */
@@ -11924,7 +11935,7 @@
     if (XOTclObjectIsClass(object)) {
       cl = (XOTclClass *)object;
     } else {
-      return XOTclObjErrType(interp, object->cmdName, "class");
+      return XOTclObjErrType(interp, object->cmdName, "class", "");
     }
 
     if (value == NULL) {
@@ -11944,7 +11955,7 @@
 
   case RelationtypeSuperclassIdx:
     if (!XOTclObjectIsClass(object))
-      return XOTclObjErrType(interp, object->cmdName, "class");
+      return XOTclObjErrType(interp, object->cmdName, "class", "");
     cl = (XOTclClass *)object;
     if (value == NULL) {
       return ListSuperclasses(interp, cl, NULL, 0);
@@ -11967,15 +11978,15 @@
     XOTclClass *metaClass;
 
     if (!XOTclObjectIsClass(object))
-      return XOTclObjErrType(interp, object->cmdName, "class");
+      return XOTclObjErrType(interp, object->cmdName, "class", "");
     cl = (XOTclClass *)object;
 
     if (value == NULL) {
       return XOTclVarErrMsg(interp, "metaclass must be specified as third argument",
                             (char *) NULL);
     }
     GetClassFromObj(interp, value, &metaClass, 0);
-    if (!metaClass) return XOTclObjErrType(interp, value, "class");
+    if (!metaClass) return XOTclObjErrType(interp, value, "class", "");
 
     cl->object.flags |= XOTCL_IS_ROOT_CLASS;
     metaClass->object.flags |= XOTCL_IS_ROOT_META_CLASS;
Index: generic/xotcl.decls
===================================================================
diff -u -r1c11937f4f0aea905fbedfbb9c2d1782b08833f5 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/xotcl.decls	(.../xotcl.decls)	(revision 1c11937f4f0aea905fbedfbb9c2d1782b08833f5)
+++ generic/xotcl.decls	(.../xotcl.decls)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -122,7 +122,7 @@
    int XOTclErrBadVal_(Tcl_Interp *interp, char *expected, char *value)
 }
 declare 28 generic {
-    int XOTclObjErrType(Tcl_Interp *interp, Tcl_Obj *nm, char *wt)
+    int XOTclObjErrType(Tcl_Interp *interp, Tcl_Obj *nm, char *wt, char *parameterName)
 }
 declare 29 generic {
     void XOTclStackDump (Tcl_Interp *interp)
Index: generic/xotclDecls.h
===================================================================
diff -u -r1c11937f4f0aea905fbedfbb9c2d1782b08833f5 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/xotclDecls.h	(.../xotclDecls.h)	(revision 1c11937f4f0aea905fbedfbb9c2d1782b08833f5)
+++ generic/xotclDecls.h	(.../xotclDecls.h)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -154,7 +154,7 @@
 #define XOTclObjErrType_TCL_DECLARED
 /* 28 */
 EXTERN int		XOTclObjErrType (Tcl_Interp * interp, Tcl_Obj * nm, 
-				char * wt);
+				char * wt, char * parameterName);
 #endif
 #ifndef XOTclStackDump_TCL_DECLARED
 #define XOTclStackDump_TCL_DECLARED
@@ -282,7 +282,7 @@
     int (*xOTclErrInProc) (Tcl_Interp * interp, Tcl_Obj * objName, Tcl_Obj * clName, char * procName); /* 25 */
     void *reserved26;
     int (*xOTclErrBadVal_) (Tcl_Interp * interp, char * expected, char * value); /* 27 */
-    int (*xOTclObjErrType) (Tcl_Interp * interp, Tcl_Obj * nm, char * wt); /* 28 */
+    int (*xOTclObjErrType) (Tcl_Interp * interp, Tcl_Obj * nm, char * wt, char * parameterName); /* 28 */
     void (*xOTclStackDump) (Tcl_Interp * interp); /* 29 */
     void (*xOTclCallStackDump) (Tcl_Interp * interp); /* 30 */
     void *reserved31;
Index: generic/xotclError.c
===================================================================
diff -u -rc6066a15de738754028991b2b57b8f1d5a1cccaa -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/xotclError.c	(.../xotclError.c)	(revision c6066a15de738754028991b2b57b8f1d5a1cccaa)
+++ generic/xotclError.c	(.../xotclError.c)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -108,9 +108,11 @@
 }
 
 extern int
-XOTclObjErrType(Tcl_Interp *interp, Tcl_Obj *value, char *type) {
+XOTclObjErrType(Tcl_Interp *interp, Tcl_Obj *value, char *type, char *parameterName) {
   Tcl_ResetResult(interp);
   Tcl_AppendResult(interp,"expected ", type, " but got \"",  ObjStr(value), "\"", 
+                   parameterName ? " for parameter " : "",
+                   parameterName ? parameterName : "",
                    (char *) NULL);
   return TCL_ERROR;
 }
Index: generic/xotclMetaData.c
===================================================================
diff -u -r2111020b49da8ce57758e51accf0b6073037f0d2 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- generic/xotclMetaData.c	(.../xotclMetaData.c)	(revision 2111020b49da8ce57758e51accf0b6073037f0d2)
+++ generic/xotclMetaData.c	(.../xotclMetaData.c)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -88,7 +88,7 @@
   int result = TCL_OK;
   int oc; Tcl_Obj* *ov; int i;
 
-  if (!obj) return XOTclObjErrType(interp, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(interp, obj->cmdName, "Object", "");
   if (objc < 2)
     return XOTclObjErrArgCnt(interp,obj->cmdName,
 				  "metadata ?(add|remove)? metaDataList");
Index: library/store/XOTclGdbm/xotclgdbm.c
===================================================================
diff -u -r1c11937f4f0aea905fbedfbb9c2d1782b08833f5 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- library/store/XOTclGdbm/xotclgdbm.c	(.../xotclgdbm.c)	(revision 1c11937f4f0aea905fbedfbb9c2d1782b08833f5)
+++ library/store/XOTclGdbm/xotclgdbm.c	(.../xotclgdbm.c)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -34,7 +34,7 @@
   XOTcl_Object* obj = (XOTcl_Object*) cd;
   int flags, block_size, mode;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 2)
     return XOTclObjErrArgCnt(in, obj->cmdName, "open filename");
 
@@ -71,7 +71,7 @@
   db_t *db;
   XOTcl_Object* obj = (XOTcl_Object *) cd;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "close");
     
@@ -94,7 +94,7 @@
   Tcl_DString result;
   datum del, key;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "names");
   
@@ -131,7 +131,7 @@
   db_t *db;
   datum key, content;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc <2 || objc > 3)
     return XOTclObjErrArgCnt(in, obj->cmdName, "set key ?value?");
 
@@ -177,7 +177,7 @@
   db_t *db;
   datum key;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 2)
     return XOTclObjErrArgCnt(in, obj->cmdName, "exists variable");
 
@@ -204,7 +204,7 @@
   datum key;
   int ret;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 2)
     return XOTclObjErrArgCnt(in, obj->cmdName, "unset key");
   
@@ -232,7 +232,7 @@
   db_t *db;
   datum key;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "firstkey");
   
@@ -270,7 +270,7 @@
   db_t *db;
   datum  newkey;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "nextkey");
   
Index: library/store/XOTclSdbm/xotclsdbm.c
===================================================================
diff -u -r1c11937f4f0aea905fbedfbb9c2d1782b08833f5 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- library/store/XOTclSdbm/xotclsdbm.c	(.../xotclsdbm.c)	(revision 1c11937f4f0aea905fbedfbb9c2d1782b08833f5)
+++ library/store/XOTclSdbm/xotclsdbm.c	(.../xotclsdbm.c)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -36,7 +36,7 @@
   for (i=0; i< objc; i++)
     fprintf(stderr, "   objv[%d]=%s\n",i,TclObjStr(objv[i]));
 */
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 2)
     return XOTclObjErrArgCnt(in, obj->cmdName, "open filename");
 
@@ -114,7 +114,7 @@
   db_t *db;
   XOTcl_Object* obj = (XOTcl_Object *) cd;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "close");
 
@@ -139,7 +139,7 @@
   Tcl_DString result;
   datum key;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "names");
 
@@ -174,7 +174,7 @@
   db_t *db;
   datum key, content;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc <2 || objc > 3)
     return XOTclObjErrArgCnt(in, obj->cmdName, "set key ?value?");
 
@@ -223,7 +223,7 @@
   db_t *db;
   datum key, content;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 2)
     return XOTclObjErrArgCnt(in, obj->cmdName, "exists variable");
 
@@ -250,7 +250,7 @@
   datum key;
   int ret;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 2)
     return XOTclObjErrArgCnt(in, obj->cmdName, "unset key");
 
@@ -287,7 +287,7 @@
   db_t *db;
   datum key;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "firstkey");
 
@@ -315,7 +315,7 @@
   db_t *db;
   datum  newkey;
 
-  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object");
+  if (!obj) return XOTclObjErrType(in, obj->cmdName, "Object", "");
   if (objc != 1)
     return XOTclObjErrArgCnt(in, obj->cmdName, "nextkey");
 
Index: tests/parameters.xotcl
===================================================================
diff -u -r464811a4aaa475de10e834b0a009521446163fc0 -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- tests/parameters.xotcl	(.../parameters.xotcl)	(revision 464811a4aaa475de10e834b0a009521446163fc0)
+++ tests/parameters.xotcl	(.../parameters.xotcl)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -180,7 +180,7 @@
 ? {D create d1} "::d1 configure: required argument 'd' is missing" "check error msg"
 
 ? {D create d2 -d x -b a} \
-    {expected boolean value but got "a"} \
+    {expected boolean value but got "a" for parameter -b} \
     "create d2 without required argument given"
 
 D create d1 -d 1
@@ -193,31 +193,31 @@
     "call method without a required argument"
 
 ? {d1 foo -r a} \
-    {expected integer but got "a"} \
+    {expected integer but got "a" for parameter -r} \
     "required argument is not integer"
 
 ? {d1 foo -r 1} \
-    {expected integer but got "aaa"} \
+    {expected integer but got "aaa" for parameter -x} \
     "default value is not of type integer"
 
 ? {d1 foo -r 1 -x 1 -object d1} \
     "" \
     "pass object"
 
 ? {d1 foo -r 1 -x 1 -object d11} \
-    {expected object but got "d11"} \
+    {expected object but got "d11" for parameter -object} \
     "pass non-existing object"
 
 ? {d1 foo -r 1 -x 1 -class D} \
     "" \
     "pass class"
 
 ? {d1 foo -r 1 -x 1 -class d1} \
-    {expected class but got "d1"} \
+    {expected class but got "d1" for parameter -class} \
     "pass object instead of class"
 
 ? {d1 foo -r 1 -x 1 -class D11} \
-    {expected class but got "D11"} \
+    {expected class but got "D11" for parameter -class} \
     "pass non-existing class"
 
 ? {D method foo {a:relation} {}} \
@@ -229,7 +229,7 @@
     "allow 'string is XXXX' for argument checking"
 ? {d1 foo 1} 1 "check int as double"
 ? {d1 foo 1.1} 1.1 "check double as double"
-? {d1 foo 1.1a} {expected double but got "1.1a"} "check non-double as double"
+? {d1 foo 1.1a} {expected double but got "1.1a" for parameter a} "check non-double as double"
 ? {D info method parameter foo} a:double
 
 #######################################################
@@ -263,7 +263,7 @@
 ? {d1 foo 1} "1" "single value"
 ? {d1 foo {1 2}} "1 2" "multiple values"
 ? {d1 foo {1 a 2}} \
-    {invalid value in "1 a 2": expected integer but got "a"} \
+    {invalid value in "1 a 2": expected integer but got "a" for parameter m} \
     "multiple values with wrong value"
 
 D method foo {m:object,multivalued} {
@@ -272,18 +272,18 @@
 ? {d1 foo ""} "" "emtpy list"
 ? {d1 foo o} "o" "single value"
 ? {d1 foo {o d1 x}} \
-    {invalid value in "o d1 x": expected object but got "x"} \
+    {invalid value in "o d1 x": expected object but got "x" for parameter m} \
     "multiple values"
 
 Class create Foo -parameter {
   {ints:integer,multivalued}
 }
 ? {Foo create foo -ints {1 2}} "::foo"
-? {Foo create foo -ints {1 a 2}} {invalid value in "1 a 2": expected integer but got "a"}
+? {Foo create foo -ints {1 a 2}} {invalid value in "1 a 2": expected integer but got "a" for parameter -ints}
 
 Foo create foo -ints {1 2}
 ? {foo ints add 0} "0 1 2"
-? {foo ints add a} {expected integer but got "a"}
+? {foo ints add a} {expected integer but got "a" for parameter value}
 
 #######################################################
 # subst default tests
@@ -519,20 +519,20 @@
 
 ? {d1 foo-base ::xotcl2::Object} "::xotcl2::Object"
 ? {d1 foo-base C} \
-    "Value 'C' of x is not a baseclass" \
+    {expected baseclass but got "C" for parameter x} \
     "not a base class"
 
 ? {d1 foo-class D} "D"
 ? {d1 foo-class xxx} \
-    {expected class but got "xxx"} \
+    {expected class but got "xxx" for parameter x} \
     "not a class"
 ? {d1 foo-class o} \
-    {expected class but got "o"} \
+    {expected class but got "o" for parameter x} \
     "not a class"
 
 ? {d1 foo-meta ::xotcl2::Class} "::xotcl2::Class"
 ? {d1 foo-meta ::xotcl2::Object} \
-    "Value '::xotcl2::Object' of x is not a metaclass" \
+    {expected metaclass but got "::xotcl2::Object" for parameter x} \
     "not a base class"
 
 ? {d1 foo-hasmixin c1} "c1"
@@ -542,13 +542,13 @@
 
 ? {d1 foo-object o} "o"
 ? {d1 foo-object xxx} \
-    {expected object but got "xxx"} \
+    {expected object but got "xxx" for parameter x} \
     "not an object"
 
 ? {d1 foo-type d1} "d1"
 ? {d1 foo-type c1} "c1"
 ? {d1 foo-type o} \
-    {expected object of type ::C but got "o"} \
+    {expected object of type ::C but got "o" for parameter x} \
     "o not of type ::C"
 
 #######################################################
@@ -578,17 +578,17 @@
 
 ? {s1 bar} 1
 ? {s1 bar 3} 3
-? {s1 bar a} {expected integer but got "a"}
+? {s1 bar a} {expected integer but got "a" for parameter y}
 
-? {s1 baz} {expected integer but got "b"}
+? {s1 baz} {expected integer but got "b" for parameter x}
 ? {s1 baz 20} 20
 s1 y 100
 ? {s1 baz} 100
 ? {s1 baz 101} 101
 
 ? {s1 boz} {1 2 3}
 s1 z {1 x 100}
-? {s1 boz} {invalid value in "1 x 100": expected integer but got "x"}
+? {s1 boz} {invalid value in "1 x 100": expected integer but got "x" for parameter x}
 ? {s1 boz {100 200}} {100 200}
 
 set aaa 100
@@ -650,24 +650,24 @@
 
 ? {ParamTest create p -o o} ::p
 ? {ParamTest create p -o xxx} \
-    {expected object but got "xxx"} \
+    {expected object but got "xxx" for parameter -o} \
     "not an object"
 
 ? {ParamTest create p -c C} ::p "class"
 ? {ParamTest create p -c o} \
-    {expected class but got "o"} \
+    {expected class but got "o" for parameter -c} \
     "not a class"
 
 ? {ParamTest create p -c1 MC1} ::p "instance of meta-class MC"
 ? {ParamTest create p -c1 C} \
-    {expected class of type ::MC but got "C"} \
+    {expected class of type ::MC but got "C" for parameter -c1} \
     "not an instance of meta-class MC"
 
 ? {ParamTest create p -d d1} ::p
 ? {ParamTest create p -d1 d1} ::p
 ? {ParamTest create p -d c1} ::p
 ? {ParamTest create p -d o} \
-    {expected object of type ::C but got "o"} \
+    {expected object of type ::C but got "o" for parameter -d} \
     "o not of type ::C"
 
 ? {ParamTest create p -mix c1} ::p
@@ -676,9 +676,9 @@
     "does not have mixin M"
 
 ? {ParamTest create p -u A} ::p
-? {ParamTest create p -u c1} {expected upper but got "c1"}
+? {ParamTest create p -u c1} {expected upper but got "c1" for parameter -u}
 ? {ParamTest create p -us {A B c}} \
-    {invalid value in "A B c": expected upper but got "c"}
+    {invalid value in "A B c": expected upper but got "c" for parameter -us}
 ? {ParamTest create p -us {A B}} ::p
 ? {p us add C end} "A B C"
 
@@ -698,7 +698,7 @@
     "o" \
     "value is an object"
 ? {p o xxx} \
-    {expected object but got "xxx"} \
+    {expected object but got "xxx" for parameter value} \
     "value is not an object"
 
 ParamTest slots {
@@ -713,7 +713,7 @@
     "value is a list of objects (multiple elements)"
 
 ? {p os {o xxx d1}} \
-    {invalid value in "o xxx d1": expected object but got "xxx"} \
+    {invalid value in "o xxx d1": expected object but got "xxx" for parameter value} \
     "list with invalid object"
 
 #######################################################
Index: tests/slottest.xotcl
===================================================================
diff -u -r147831f1098cb9b96a28d4d5b0f9f3ccea35b9da -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- tests/slottest.xotcl	(.../slottest.xotcl)	(revision 147831f1098cb9b96a28d4d5b0f9f3ccea35b9da)
+++ tests/slottest.xotcl	(.../slottest.xotcl)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -392,7 +392,7 @@
 
 Person p2 -name "Gustaf"
 p2 projects add ::project1
-? {p2 projects add ::o1} {expected object of type ::Project but got "::o1"}
+? {p2 projects add ::o1} {expected object of type ::Project but got "::o1" for parameter value}
 p2 salary 100
 ? {catch {p2 salary 100.9}} 1
 ? {p2 salary} 100
Index: tests/testx.xotcl
===================================================================
diff -u -r48d5751e9aeb6a4f388f6531a9248c1847b22cae -rc942f4e117d2aa3c8594702e0476a3f73a4147df
--- tests/testx.xotcl	(.../testx.xotcl)	(revision 48d5751e9aeb6a4f388f6531a9248c1847b22cae)
+++ tests/testx.xotcl	(.../testx.xotcl)	(revision c942f4e117d2aa3c8594702e0476a3f73a4147df)
@@ -3985,7 +3985,7 @@
     catch {
 	o z3 -b abc -- -b
     } m
-  errorCheck $m {expected boolean value but got "abc"} "not boolean"
+  errorCheck $m {expected boolean value but got "abc" for parameter -b} "not boolean"
 
     set ::r ""    
     #o z4 -c 1 1