Add a Profile Tab page at the developer page (Edit Settings > Profile) http://www.facebook.com/developers/apps.php
You can add all Apps as Tab which are currently active in your session and have Tabs-Urls added.
Use the "+" icon at the Public Profile/Page to add it - if its not in the list use the search function at the bottom of the list.
If you're Tab is blank open the Tab Url directly. If its not working there fix it until it is. If it is working there the problem is within the communication of fb with your host. Check your Logfiles!
Wild guess:
Be aware that facebook fetches this pages via POST request. I had a nasty bug because nginx 500's all post requests to static files (e.g. HTML files).