[Charlie98902]

I've just fixed it myself based on what Mystics said:

Comment out line 317 to 320 in showthread.php.

PHP Code:

//if ($thread['forumid'] == $vbulletin->options['vbcmsforumid'] AND !can_moderate($thread['forumid']))
//{
    //eval(standard_error(fetch_error('invalid_comment_forum', $vbphrase['forum'], $vbulletin->options['contactuslink'])));
//} 


Now open forumdisplay.php, scroll down to line 138.

Replace the following

PHP Code:

if (!$foruminfo['forumid'] OR ($foruminfo['forumid'] == $vbulletin->options['vbcmsforumid'] AND !can_moderate($foruminfo['forumid']))) 


with this:

PHP Code:

//if (!$foruminfo['forumid'] OR ($foruminfo['forumid'] == $vbulletin->options['vbcmsforumid'] AND !can_moderate($foruminfo['forumid'])))
if (!$foruminfo['forumid']) 


You will have to do this if you upgrade your forum again or when ever you replace the showthread.php and forumdisplay.php files. Hopefully next release vbulletin team creates an on/off switch for this.