Didn't know where to put this, so trying in here.
If you are in a subforum and select the Forum selection (as an example from here, it shows Forum > Forum / Directory News & Information / Advertisers Areas / Forum Suggestions) clicking on the first 'Forum' link gives the following error:

Warning: require(/home/mobile/public_html/forum/wp-blog-header.php) [function.require]: failed to open stream: No such file or directory in /home/mobile/public_html/forum/index.php on line 19

Fatal error: require() [function.require]: Failed opening required '/home/mobile/public_html/forum/wp-blog-header.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/mobile/public_html/forum/index.php on line 19

If you select Forum from the top of the page (Next to Disco Directory) you navigate to the forum as expected