Index: openacs-4/packages/acs-lang/tcl/lang-message-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-lang/tcl/lang-message-procs.tcl,v
diff -u -r1.33 -r1.34
--- openacs-4/packages/acs-lang/tcl/lang-message-procs.tcl	16 Oct 2003 10:50:12 -0000	1.33
+++ openacs-4/packages/acs-lang/tcl/lang-message-procs.tcl	22 Oct 2003 16:52:23 -0000	1.34
@@ -267,7 +267,11 @@
                 # from scope calling lang::message::lookup
                 upvar $upvar_level $variable_key variable_value
 
-                append formated_message $variable_value
+                if { [info exists variable_value] } {
+                    append formated_message $variable_value
+                } else {
+                    error "Message contains a variable named '$variable_key' which doesn't exist in the caller's environment"
+                }
             }
         }
     }