Facebooks credentials are not correct for website login

Stefan,
After you register with Facebook, how are you trying to re-login? You should be clicking the "Facebook" login button. Your Facebook credentials will not work in the username/password form of the SCLogin module.

For the password, please check if you have the "Generate Random Password" setting enabled in the Configuration -> General section of JFBConnect. When enabled, your new user account email will contain your username and the random password that you can login to Joomla with using the username/password fields. If you aren't generating a password for your users, they will only be able to login with their social network credentials. It's up to you whether you want to give them the option to login to Joomla directly.

I hope that helps explain,
Alex