diff -Naur drupal6.orig/includes/common.inc drupal6/includes/common.inc
--- drupal6.orig/includes/common.inc	2007-05-04 12:41:36.000000000 +0300
+++ drupal6/includes/common.inc	2007-05-09 16:56:13.000000000 +0300
@@ -343,6 +343,9 @@
   if ($path && $path != $_GET['q']) {
     menu_set_active_item($path);
     $return = menu_execute_active_handler();
+    if ($return == MENU_NOT_FOUND) {
+      $return = '';
+    }
   }
   else {
     // Redirect to a non-existent menu item to make possible tabs disappear.
@@ -373,6 +376,9 @@
   if ($path && $path != $_GET['q']) {
     menu_set_active_item($path);
     $return = menu_execute_active_handler();
+    if ($return == MENU_ACCESS_DENIED) {
+      $return = '';
+    }
   }
   else {
     // Redirect to a non-existent menu item to make possible tabs disappear.