Index: wp-includes/nav-menu-template.php
===================================================================
--- wp-includes/nav-menu-template.php	(revision 24432)
+++ wp-includes/nav-menu-template.php	(working copy)
@@ -433,6 +433,7 @@
 					'post_type' == $parent_item->type &&
 					! empty( $queried_object->post_type ) &&
 					is_post_type_hierarchical( $queried_object->post_type ) &&
+					is_array( $queried_object->ancestors ) && 
 					in_array( $parent_item->object_id, $queried_object->ancestors ) &&
 					$parent_item->object != $queried_object->ID
 				) ||
@@ -441,6 +442,7 @@
 				(
 					'taxonomy' == $parent_item->type &&
 					isset( $possible_taxonomy_ancestors[ $parent_item->object ] ) &&
+					is_array( $possible_taxonomy_ancestors[ $parent_item->object ] ) && 
 					in_array( $parent_item->object_id, $possible_taxonomy_ancestors[ $parent_item->object ] ) &&
 					(
 						! isset( $queried_object->term_id ) ||