Index: generic/nsf.c
===================================================================
diff -u -r50d4fe25876215d2e71f39fa4e5fe7426dda4464 -rdc94a1f141b1c6a106d0ee142c9df2743ac82e67
--- generic/nsf.c	(.../nsf.c)	(revision 50d4fe25876215d2e71f39fa4e5fe7426dda4464)
+++ generic/nsf.c	(.../nsf.c)	(revision dc94a1f141b1c6a106d0ee142c9df2743ac82e67)
@@ -29089,7 +29089,7 @@
     } else {
       char *errMsg = ObjStr(Tcl_GetObjResult(interp));
 
-      if (*errMsg != '\0') {
+      if (*errMsg == '\0') {
         return NsfPrintError(interp, "invalid value constraints \"%s\"",
                              ObjStr(paramObjPtr) );
       } else {
Index: tests/disposition.test
===================================================================
diff -u -rc4f449cb353be812ba6502ef8e9587e87881f59b -rdc94a1f141b1c6a106d0ee142c9df2743ac82e67
--- tests/disposition.test	(.../disposition.test)	(revision c4f449cb353be812ba6502ef8e9587e87881f59b)
+++ tests/disposition.test	(.../disposition.test)	(revision dc94a1f141b1c6a106d0ee142c9df2743ac82e67)
@@ -47,7 +47,7 @@
     #
     # Not applicable in parametercheck
     #
-    ? [list ::nsf::is $paramType $msg] "invalid value constraints \"$paramType\""
+    ? [list ::nsf::is $paramType $msg] "invalid value constraints \"$paramType\": parameter option '$paramType' not allowed"
   }
 
   
@@ -141,16 +141,10 @@
   #
   # Without the sketched extension, one could use eval in a forwarder.
   # 
-puts stderr ===1
   C setObjectParams {{{-multi-2:forward,method=eval %self %method}}}
-puts stderr ===2a
-set x [C new -multi-2 {X Y}]
-puts stderr [$x eval {set :multi-2}]
-puts stderr ===2b
 
   ? {[C new -multi-2 {X Y}] eval {set :multi-2}} \
       "X Y"
-puts stderr ===3
 
   #
   # In the positional case, why is FOO not passed on as arg value to
@@ -406,7 +400,8 @@
     initcmd
   } {
     ::nsf::method::property R $methods(raz) returns $dispoSpec
-    ? {R raz} "invalid value constraints \"$dispoSpec\""
+    set trueSpec [lindex $dispoSpec 0]
+    ? {R raz} "invalid value constraints \"$dispoSpec\": parameter option '$trueSpec' not allowed"
   }
   
 
Index: tests/parameters.test
===================================================================
diff -u -rb6fa800493538a2f179224f7f1717eb70913dd8b -rdc94a1f141b1c6a106d0ee142c9df2743ac82e67
--- tests/parameters.test	(.../parameters.test)	(revision b6fa800493538a2f179224f7f1717eb70913dd8b)
+++ tests/parameters.test	(.../parameters.test)	(revision dc94a1f141b1c6a106d0ee142c9df2743ac82e67)
@@ -104,7 +104,7 @@
   ? {::nsf::is integer 0xy} 0
 
   # built in converter, but not allowed
-  ? {::nsf::is switch 1} {invalid value constraints "switch"}
+  ? {::nsf::is switch 1} {invalid value constraints "switch": invalid parameter type "switch" for argument "value"; type "switch" only allowed for non-positional arguments}
   ? {::nsf::is superclass M} {invalid value constraints "superclass"}
 
   # don't allow convert;