[evss]

in includes/init.php
This may solve the problem is your main domain:
www.domain.com is been redirected to your
forums.domain.com/vbindex.php


Find:

PHP Code:

$http_host = preg_replace('#^www\.#i', '', $http_host); 


Replace With:

PHP Code:

$http_host = preg_replace('#^(forum|www)\.#i', '', $http_host);