Have reviewed your installation and do not understand exactly what the issue is. I was able to successfully login with my Facebook account (user now deleted) without error. I was also able to successfully login with your very own Facebook account (user still remains). However your Administrator had the same email address as that provided by Facebook causing "This e-mail is already registered. If you forgot your password, click on the Forgot your password link and a new password will be sent to you.", which is expected. However did not receive a 100 error code.