Hey, I've heard more people have this problem. Of course you can always message Wikia staff that you have this problem via Special:Contact :)
This appears to be a problem with Wikia's implementation of Facebook connections, and possibly effects all wikis. You should Special:Contact staff immediately, as it is likely that all users who were logging in with Facebook can no longer do so until this is fixed.
Thanks. We're currently working on this issue as a top priority, and hope to get everything back to normal ASAP. Note, this issue does not affect non-Facebook Connect login attempts.