I was talking with Isaac (id242) via Google Talk earlier, and we came to the consensus that you could try making a separate UBB install in your webspace, and then if all is working well, compare the two configuration files and adjust values as needed.
You'd want to have a separate database setup for the second install, and you'll want to use a different cookie prefix for the secondary install however.
FWIW, my paths/urls on
Scouters World are:
'FULL_URL' => 'http://www.scoutersworld.com/forum',
'BASE_URL' => '/forum',
'FULL_PATH' => '/home/scout/public_html/forum',
'SESSION_PATH' => '/home/scout/public_html/forum/sessions',
'REFERERS' => 'http://www.scoutersworld.com',