Authenticated Referrals are being removed by Facebook and are no longer available to new Facebook Apps. All apps will have the feature disabled in February. For more information on the removal of Authenticated Referrals can be found in their blog post below:
developers.facebook.com/blog/post/2012/1...pps-with-open-graph/
Hope that helps explain. Unfortunately, there is no longer a way to force users to login to your site using Facebook.
Alex
Authenticated referrals vs Auth dialog
