Odd htaccess problem that I just can't pinpoint!

[4bidden]

Alright...so I just now noticed how some users are getting errors when trying to access my message forum directly.

Here is the issue.... (attention to trailing slashes)

h-ttp://www.atvdistrict.com/forum works
h-ttp://www.atvdistrict.com/forum/ works
h-ttp://atvdistrict.com/forum/ works
h-ttp://atvdistrict.com/forum does NOT work

The first 3 properly redirect to h-ttp://www.atvdistrict.com/forum/ but the last one magically send me to h-ttp://www.atvdistrict.com/forum//var/www/vhosts/atvdistrict.com/httpdocs/forum and produces a page not found error

How can I fix this one instance? Help is MUCH appreciated!

Here is the .htaccess file

RewriteEngine On

RewriteCond %{HTTP_HOST} !^www\.atvdistrict\.com
RewriteRule (.*)$ http://www.atvdistrict.com/forum/$1 [L,R=301]

RewriteRule ^((urllist|sitemap_).*\.(xml|txt)(\.gz)?)$ vbseo_sitemap/vbseo_getsitemap.php?sitemap=$1 [L]

RewriteCond %{QUERY_STRING} !vbseourl=
RewriteCond %{REQUEST_URI} !(admincp/|modcp/|chat|cron)
RewriteRule ^(.*\.php)$ vbseo.php?vbseourl=$1 [L,QSA]

RewriteCond %{REQUEST_FILENAME} !\.(jpg|gif)$
RewriteRule ^(archive/.*)$ vbseo.php?vbseourl=$1 [L,QSA]

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !^(admincp|modcp|clientscript|cpstyles|images)/
RewriteRule ^(.+)$ vbseo.php?vbseourl=$1 [L,QSA]

RewriteRule ^((urllist|sitemap).*\.(xml|txt)(\.gz)?)$ vbseo_sitemap/vbseo_getsitemap.php?sitemap=$1 [L]