Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.269
diff -u -p -r1.269 menu.inc
--- includes/menu.inc	23 Apr 2008 20:01:47 -0000	1.269
+++ includes/menu.inc	2 May 2008 12:30:06 -0000
@@ -1658,7 +1658,6 @@ function menu_router_build($reset = FALS
       $menu = $cache->data;
     }
     else {
-      db_query('DELETE FROM {menu_router}');
       // We need to manually call each module so that we can know which module
       // a given item came from.
       $callbacks = array();
@@ -1674,7 +1673,6 @@ function menu_router_build($reset = FALS
       // Alter the menu as defined in modules, keys are like user/%user.
       drupal_alter('menu', $callbacks);
       $menu = _menu_router_build($callbacks);
-      cache_set('router:', $menu, 'cache_menu');
     }
   }
   return $menu;
@@ -2254,6 +2252,15 @@ function _menu_router_build($callbacks) 
   }
   array_multisort($sort, SORT_NUMERIC, $menu);
 
+  if ($menu) {
+    // Only delete the existing router if we have data to replace it.
+    db_query('DELETE FROM {menu_router}');
+  }
+  else {
+    // We must have a serious error.
+    watchdog('php', 'Menu router rebuild faild - some paths may not work correctly.', array(), WATCHDOG_ERROR);
+    return array();
+  }
   // Apply inheritance rules.
   foreach ($menu as $path => $v) {
     $item = &$menu[$path];
@@ -2356,6 +2363,7 @@ function _menu_router_build($callbacks) 
   $masks = array_keys($masks);
   rsort($masks);
   variable_set('menu_masks', $masks);
+  cache_set('router:', $menu, 'cache_menu');
   return $menu;
 }