Chdir problem

I use this code to include some vBulletin files in my post.php

chdir(‘../forums/’);
require_once(‘global.php’);
require_once(‘includes/functions_newpost.php’);

chdir(‘../wp-admin/’);
require_once(‘admin.php’);

But after editing a post it does not redirect back to the WordPress admin page, it just goes to a blank page. The post is still edited, but again, redirection is broken.

Also, the code works fine on my local server running PHP5. This server is running PHP4 however. I really don’t see why that’d make a difference in this case though…