Index: wp-includes/nav-menu.php
===================================================================
--- wp-includes/nav-menu.php	(revision 17660)
+++ wp-includes/nav-menu.php	(working copy)
@@ -559,8 +559,11 @@
 			$menu_item->type = empty( $menu_item->type ) ? get_post_meta( $menu_item->ID, '_menu_item_type', true ) : $menu_item->type;
 
 			if ( 'post_type' == $menu_item->type ) {
-				$object = get_post_type_object( $menu_item->object );
-				$menu_item->type_label = $object->labels->singular_name;
+				if ( post_type_exists( $menu_item->object ) )
+					$menu_item->type_label = get_post_type_object( $menu_item->object )->labels->singular_name;
+				else
+					$menu_item->type_label = $menu_item->object;
+
 				$menu_item->url = get_permalink( $menu_item->object_id );
 
 				$original_object = get_post( $menu_item->object_id );
@@ -568,8 +571,11 @@
 				$menu_item->title = '' == $menu_item->post_title ? $original_title : $menu_item->post_title;
 
 			} elseif ( 'taxonomy' == $menu_item->type ) {
-				$object = get_taxonomy( $menu_item->object );
-				$menu_item->type_label = $object->labels->singular_name;
+				if ( taxonomy_exists( $menu_item->object ) )
+					$menu_item->type_label = get_taxonomy( $menu_item->object )->labels->singular_name;
+				else
+					$menu_item->type_label = $menu_item->object;
+
 				$term_url = get_term_link( (int) $menu_item->object_id, $menu_item->object );
 				$menu_item->url = !is_wp_error( $term_url ) ? $term_url : '';