I've gotten a couple of reports of an error when trying to log in using your Facebook Connect accounts.
REST API is deprecated for versions v2.1 and higher (12)
I've sent the information over to the web team and they are going to be taking a look at the cause and hopefully have some information about what is causing this as well as a solution in the near future. I'll keep you updated as I learn more information.
This is now solved. Facebook Connect required some changes before they would allow the login process to work with sites like ours. We've made the changes that are now required with this update.
You should now be able to connect using your login as before.
Sorry for the inconvenience that you may have encountered.