Now I just tried to login again, with the username and password which I filled in like an hour ago (they were still saved) and now the login worked. So maybe It was just a network issue.
Since I don't know how your plans for the login are. Wouldn't a account with a email adress be worth a thought? This would make this whole discussion be useless, because I could just reset the password.
I don't want to critisize anythink, it is just a suggestion.