I found a solution which worked for me.
- Delete all in the QMC configured DSCs
- Kill the Directory Service Connector Service via TaskManager or Services
- Restart the Service
- Configure all DSCs again
I still don´t know what caused the problem. I just wanted to set the cache expiration from 15 minutes to 5 and everything stoped working. Stuff like this, the last NPrinting release, the initial QlikView 12 release and so on makes me really question if qlikview is really "business ready" and if qlik has any testers at all....