FIBS login with 3-letter login name fails

[siteswapper]

My FIBS login name has only three letters, and when I try to login, I get the following error message:
Generic error, please retype username and password

When I use an arbitrary username with 4 letters, the error message is
user not known or wrong password
So something went wrong before the login even happened.
Btw, a password with less than 4 letters gets cought by the mask.

Thank you! :-)