DeFender, let me explain how our FB Connect plugin works. Our system needs the username to add a new user, but the Facebook have no such field, so the plugin grabs the First name and the Last name and then composes the username for our system.
And if the First name or the Last name are contain non latin symbols then the system can't parse them. Before it crashed with an error, but now we have fixed it by replacing the missing name by the user_{$userId} value.