Index: wp-admin/includes/menu.php
===================================================================
--- wp-admin/includes/menu.php	(revision 18436)
+++ wp-admin/includes/menu.php	(working copy)
@@ -216,10 +216,14 @@
 
 // Remove the last menu item if it is a separator.
 $last_menu_key = array_pop( array_keys( $menu ) );
-if ( 'wp-menu-separator' == $menu[ $last_menu_key ][ 4 ] )
-	unset( $menu[ $last_menu_key ] );
-unset( $last_menu_key );
 
+if( ! is_null( $last_menu_key ) )
+{
+    if ( 'wp-menu-separator' == $menu[ $last_menu_key ][ 4 ] )
+	    unset( $menu[ $last_menu_key ] );
+    unset( $last_menu_key );
+}
+
 if ( !user_can_access_admin_page() ) {
 	do_action('admin_page_access_denied');
 	wp_die( __('You do not have sufficient permissions to access this page.') );