--- a/web/uicfg.py	Thu Aug 26 11:45:57 2010 +0200
+++ b/web/uicfg.py	Mon Sep 06 15:03:11 2010 +0200
@@ -407,7 +407,7 @@
 
     def tag_relation(self, key, tag):
         for tagkey in tag.iterkeys():
-            assert tagkey in self._keys
+            assert tagkey in self._keys, 'tag %r not in accepted tags: %r' % (tag, self._keys)
         return super(_ReleditTags, self).tag_relation(key, tag)
 
 reledit_ctrl = _ReleditTags('reledit')