qmasterd process doesn't run as root

I've just installed Compressor 4.0.2 on three of my laptops. On my main working computer Compressor refuses to work as the master. On my two other computers it works just fine with identical settings. I found out that on these two Macs the process qmasterd runs as root permanently (also when Compressor is not running) whereas on the "problem" Mac it runs with my user previleges. The process disappears when I quit Compressor on this machine. Activity Monitor tells me that qmasterd was started by launchd (on the two other Macs) and by Compressor itself (on the "problem" Mac).

I reinstalled Compressor and ran "Compressor Repair" with no success. I reinstalled MacOS 10.7.3, disabled the firewall, repaired permissions, used ethernet and WIFI connections, nothing. I read so many forum posts which don't give any solution for my problem.

When I try to form a cluster on the "problem" Mac an error comes up: "SwampDaemon::NFSPublisher: authorization has expired". Sometimes there is no error message at all.

Remember: With identical settings Compressor works as expected on two other Macs.