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"