Saturn, sorry that I wasn't clear. I guess what happened is this: I had first installed KP50, Cleven and the backports-modules-power, so the backports went to /opt/lib/modules/2.6.28.10-power50/ back then. Afterwards, I installed kernel-cssu and while the backports-modules stayed at /opt/lib/modules/2.6.28.10-power50/, Cleven now searched for them in /opt/lib/modules/2.6.28.10-cssu1/ even though that directory doesn't exist.