eM Client fails authentication at startup

Hi forum,

after starting the client I get an error message saying

“Server saying: Authorization required”

The thing is that username and password are correct.
After I cancel this window (because clicking on “ok” won’t remove it) the program works perfectly fine…

I have had this problem half a year ago and solved it back then but I can’t remember how. Unfortunately my system crashed and I had to set up everything new.

Does anyone know something about this annoying error?

Thanks in advance