Codeigniter + Facebook integration issues

[eluser]Unknown[/eluser]
OK I've been trying to make by first Facebook app with CI and I'm almost about to give up and use plain PHP. But before that I might as well ask for help :-)

The app is currently sitting at http://apps.facebook.com/try-to-pronounce-it
Make sure you are logged out of Facebook before visiting that link. Once you visit it it'll ask you to log in to use the app.

Once you log in you will see a 404 error. That is the problem.

However, if you remove the the query string in the URL (i.e. the question mark and thereafter) the app will start working.

It seems like CI "cares" about the query string. Is there a way I can strip the query string or something?

Btw after hours of messing around I've set the uri protocol in the config.php to REQUEST_URI. AUTO and PATH_INFO both don't work. Also I'm using nginx and not Apache as the web server but I really really doubt that's the problem.

Thanks for any help.

EDIT: This is an FBML app, if that makes any difference :/