I'm running Ultimate Facebook 2.6.2, WordPress 3.5.1 (with multisite) and BuddyPress 1.6.4.
Ultimate Facebook is correctly configured and most of the features are working as intended (importing Facebook comments, etc.). Facebook Connect, however, is having some problems. Here's a screenshot of the configuration: http://i.imgur.com/MqOSOWJ.png
The problem is that when "Login with Facebook" is clicked, it loads for a couple of seconds and then redirects to a 404 at http://SITEURL/members//profile/edit (i.e. the "USER_LOGIN" macro is coming up with a blank). No user is being created in the database.
I have tried disabling Ultimate Facebook and testing other Facebook Connect plugins (principally Nextend Facebook Connect), and they are successfully creating users in the database, but they have other problems with the redirect that make me prefer Ultimate Facebook.
Any ideas? Please let me know if there's anything I need to send you (including dashboard access) that might help you.