Drupal for Facebook comes with a README.txt. This file is more up-to-date than the page you are reading now. Read it from start to finish, carefully. This is guaranteed to save you time in the long run.
The project issue queue is another place to look for answers. Probably, you're not the first to encounter your problem. If you're lucky enough to be first, save others time by describing your problem on the issue queue.
If you can't access the page or are getting some funky errors try these:
- You are not logged into facebook
- You haven't enabled the FBML Theme
- Your facebook API key, Secret key, or canvass page are incorrect
- You didn't download and install the correct facebook-platform
Facebook now allows users to see canvas pages , even if you're not logged in to facebook, however, it can cause issues with Drupal. Check to make sure that you are logged into facebook, and that your Application settings in Drupal are correct, especially "Require Login:".
The FBML theme allows your site to serve up pages in the FBML (FaceBook Markup Language). FBML is like html with certain restrictions and added features specific to facebook. The theme is included with the module, but it has to be moved to a themes folder. Even then, Drupal will not recognize it until the themes list cache is refreshed. To do this, simply visit the administrative page which shows the themes list. It is not necessary to enable the fb_fbml theme. See the installation instructions above.
Double check that you have registered your application at developer.facebook.com, and that you have entered the correct values in drupal.