Hei, just checked and the username and password are encoded and the encoding works properly, so ä and ö should not be a problem. Long username probably is not the issue either, or at least mine is 14 characters long and is causing no problems.

If you did not already do so, could you check that you have the right username/password by going to the TVKaista site, logging out and manually entering the information in the fields at the top of the page? (I.e. do not use the Facebook/Twitter/whatever buttons.)