Index: wp-admin/includes/menu.php
===================================================================
--- wp-admin/includes/menu.php	(revision 18627)
+++ wp-admin/includes/menu.php	(working copy)
@@ -216,7 +216,7 @@
 
 // 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 ] )
+if ( !empty( $menu ) && 'wp-menu-separator' == $menu[ $last_menu_key ][ 4 ] )
 	unset( $menu[ $last_menu_key ] );
 unset( $last_menu_key );