Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.255.2.28
diff -u -p -r1.255.2.28 menu.inc
--- includes/menu.inc	9 Feb 2009 16:28:21 -0000	1.255.2.28
+++ includes/menu.inc	16 Apr 2009 10:07:30 -0000
@@ -2288,6 +2288,7 @@ function _menu_router_build($callbacks) 
     return array();
   }
   // Delete the existing router since we have some data to replace it.
+  db_query("LOCK TABLE {menu_router} WRITE");
   db_query('DELETE FROM {menu_router}');
   // Apply inheritance rules.
   foreach ($menu as $path => $v) {
@@ -2387,6 +2388,7 @@ function _menu_router_build($callbacks) 
       $item['title'], $item['title callback'], $title_arguments,
       $item['type'], $item['block callback'], $item['description'], $item['position'], $item['weight'], $item['include file']);
   }
+  db_query("UNLOCK TABLES");
   // Sort the masks so they are in order of descending fit, and store them.
   $masks = array_keys($masks);
   rsort($masks);