Well you have more problems that just the search. I tried your link which takes me to
The initial page is fine. But if I select the forum home link at the top it takes me to
Which is the wrong address( Page can't be found).
If I try to open a forum same thing it redirects to
Same thing (The page cannot be found). You need to go through the settings to correct the paths and file permissions are correct.
Possibly you got some paths mixed up with your new threads location.
If I edit the path I get a result but only if I change ultimatebb to cgi not php.
If I recall this was a setting for the accelerator? in the control panel where the main script changed to from cgi to php to increase speed. It may be this is also turned off but if paths are wrong it will never re-index to cgi.