It could be in however you did your server config that your SEO
does not work anymore.
Tell me do spider urls work?
Your forum does not appear to be using SEO
either so I wonder what would happen on your site if you try using the vb seo
feature. The only thing I know of is spider urls require AcceptPathInfo or AllowPathInfo to be on depending on what apache version you have and as far as SEO
to knowledge as long as mod rewrite is installed it should work. I mean has the server been setup to recoginise htaccess files. It can be a multitude of issues here.
The point being your server supported things fine then you reconfigured your server and now its broken. You need to look at the server config. You host might be able to assist there.