I registered and received my email, but I can’t log in, no message, it just refreshes the page. I would say it has something to do with the rewrite rules. I would turn off slugs or permalinks in your bb-config.php.
I just looked in my bb-config-sample.php though, and there is no mod_rewrite line in there? Weird. Not sure how to tell you to turn off pretty permalinks, but I suspect that’s the problem. That, or something in an .htaccess file that is causing weirdness.