I tried again and still have the same problems ...
It must be related to the new authentication procs,
I checked the tables parties, persons, users and everything seems to look okay. I changed usernames in persons to the same as the email in parties as it is when I register a new user.
I still get the error maessage Unknown username or
unknown email or invalid username or password.
Is there any dependency to the underlying plattform for the administrator?