There is a bug in the forum module:
Fatal error: Call to a member function setField() on a non-object in /sites/ssopen/www/forum/code/Forum.php on line 641
The problem is that it is not checked if $post is really set. You should at least change line 627 from
else user_error('A valid post was not specified. We pass the Post ID through now, creating a blank post on ReplyForm. Dumb, but necessary for uploading attachments.', E_USER_ERROR);
to
if(!issset($post))
user_error('A valid post was not specified. We pass the Post ID through now, creating a blank post on ReplyForm. Dumb, but necessary for uploading attachments.', E_USER_ERROR);