Index: branches/RC/core/units/general/cat_event_handler.php
===================================================================
diff -u -r10532 -r10643
--- branches/RC/core/units/general/cat_event_handler.php	(.../cat_event_handler.php)	(revision 10532)
+++ branches/RC/core/units/general/cat_event_handler.php	(.../cat_event_handler.php)	(revision 10643)
@@ -397,6 +397,10 @@
 		}
 
 		$tree_indexes = $this->Application->getTreeIndex($category_id);
+		if (!$tree_indexes) {
+			// id of non-existing category was given
+			return 'FALSE';
+		}
 
 		return TABLE_PREFIX.'Category.TreeLeft BETWEEN '.$tree_indexes['TreeLeft'].' AND '.$tree_indexes['TreeRight'];
 	}