Oops, I've been to fast...
I typed the command "kaffeine" in a console-window as superuser and kaffeine started at that moment indeed, but it started under the user "root" and that was not what I wanted to do.
Under my own username, happens nothing when I try to start kaffeine.
After that I tried the following steps:
I deleted next files
- /home/username/.kde/share/config/kaffeinerc
- /home/username/.kde/share/apps/kaffeine
- the directory /home/username/.xine
after that, I removed the whole program kaffeine and reinstalled it.
nothing of this works