Index: wp-includes/nav-menu.php
===================================================================
--- wp-includes/nav-menu.php	(revision 14071)
+++ wp-includes/nav-menu.php	(working copy)
@@ -272,7 +272,9 @@
 			$menu_item->append = strtolower( $object->singular_label );
 
 			$menu_item->title = $menu_item->name;
-			$menu_item->url = get_term_link( $menu_item, $menu_item_object );
+			
+			$term_url = get_term_link( $menu_item, $menu_item_object );
+			$menu_item->url = !is_wp_error( $term_url ) ? $term_url : '';
 			$menu_item->target = '';
 			$menu_item->attr_title = '';
 			$menu_item->description = '';