--- a/Tools__NewSystemBrowser.st	Thu Feb 26 09:01:38 2015 +0100
+++ b/Tools__NewSystemBrowser.st	Thu Feb 26 10:58:40 2015 +0100
@@ -35661,7 +35661,8 @@
     tempStream nextPutLine:('"/ first, a guard, to ignore the patch if the library already contains an up-to-date class:').
     tempStream nextPutLine:('"/').
     changedOwningClasses do:[:eachClass |
-        tempStream nextPutLine:('(''%1'' compareAsVersionNumberWith:%2 revision) < 0 ifTrue:[ InvalidPatchError raiseErrorString:''patch is for older version (%1) of class %2'' ].'
+        tempStream nextPutLine:('(Smalltalk classNamed:''%2'') isNil ifTrue:[InvalidPatchError raiseErrorString:''patch is for non-existant class %2 (probably for a plugin that is not installed)'']. 
+(''%1'' compareAsVersionNumberWith:%2 revision) < 0 ifTrue:[ InvalidPatchError raiseErrorString:''patch is for older version (%1) of class %2'' ].'
                             bindWith:eachClass revision
                             with:eachClass name).
     ].
@@ -62133,11 +62134,11 @@
 !NewSystemBrowser class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libtool/Tools__NewSystemBrowser.st,v 1.2198 2015-02-26 04:00:07 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libtool/Tools__NewSystemBrowser.st,v 1.2199 2015-02-26 09:58:40 stefan Exp $'
 !
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libtool/Tools__NewSystemBrowser.st,v 1.2198 2015-02-26 04:00:07 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libtool/Tools__NewSystemBrowser.st,v 1.2199 2015-02-26 09:58:40 stefan Exp $'
 !
 
 version_HG
@@ -62146,7 +62147,7 @@
 !
 
 version_SVN
-    ^ '$Id: Tools__NewSystemBrowser.st,v 1.2198 2015-02-26 04:00:07 cg Exp $'
+    ^ '$Id: Tools__NewSystemBrowser.st,v 1.2199 2015-02-26 09:58:40 stefan Exp $'
 ! !