Admin login on site with Facebook-only accounts



My forum has Facebook-only accounts. But admin is a local user created during bootstrap process. Its name “admin” and I don’t to make my FB-account as admin. I want to keep this “non-personal” admin. But there’re problems with login under that account.
I know that these’s a special url for such cases - /users/admin-login
It asks me “admin email” and I enter admin’s email but it won’t work - just tells me “Error!”.

What can be wrong?