Index: openacs-4/packages/xowiki/tcl/includelet-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/xowiki/tcl/includelet-procs.tcl,v
diff -u -r1.31 -r1.32
--- openacs-4/packages/xowiki/tcl/includelet-procs.tcl	26 Apr 2008 16:13:05 -0000	1.31
+++ openacs-4/packages/xowiki/tcl/includelet-procs.tcl	26 Apr 2008 16:31:47 -0000	1.32
@@ -516,10 +516,11 @@
       }
     }
 
-    #my msg "nr trees = [llength $trees] && $tree_name"
+    #my msg "nr trees = [llength $trees], tree:name = '$tree_name'"
     if {[llength $trees] == 0} {
-      # safety net
-      return ""
+      error "No category tree found\n\
+	(mapped trees = [llength $mapped_trees],\n\
+	tree_name = '$tree_name')"
     }
 
     foreach tree $trees {