Well, if you're desperate you could try this test: edit forums/global.php and find this line (near the top):
Code:
require_once(CWD . '/includes/init.php');
and above it, insert this line:
Code:
die("getcwd='$getcwd', including '" . CWD . "/includes/init.php'");
Then any page should just display the one line telling you what $getcwd is and what file it's trying to include. I'm not sure how much that will help, but if you try this let us know what it says.