So I'm trying to simply maintain user information across the site (see if the user is logged in, get the username, user id, etc) to unlock a few extra functions without having two registration/login forms. I found the code that says at the beginning of the page I add:

define('FORUM_ROOT', './forum/');
require FORUM_ROOT.'include/common.php';

Basically, it's including the common.php page just fine, but no matter what I do I keep getting the same message of:

The constant FORUM_ROOT must be defined and point to a valid PunBB installation root directory.

Despite the fact that FORUM_ROOT _IS_ defined. I'm lost, and I've tinkered with this as much as I understand...