Kaffeine is a multimedia player for KDE that uses
Xine as backend.
Maybe it you are running an unstable version or an older one, try upgrading Xine and Kaffeine to the latest stable versions.
Another good movie player is
MPlayer.
Cheers, Boby!
Edit: I had once little problems with Kaffeine, it was an testing version. Now after upgrading everything to stable versions, I like it more than a regular Xine GUI and/or Mplayer.