It's been a week. There aren't any problems accessing the rest of the site. Besides, I can pull up the first page. It's when I click on any of the links that I get the 404 error.
It looks like the site uses a url rewrite system (I do this on another site) where
http://www.domain.com/vbforum/f21/ is converted to
http://www.domain.com/vbforum/forumdisplay.php?f=21. I tested this. Replacing 'f' + topic number (f21/) with 'forumdisplay.php?f=' + topic number (forumdisplay.php?f=21) does pull up the page.
There are other redirects, and none of them seem to be working. So there's a problem with the redirects. Where do I find that code? Any idea why the move would break this part of the code?