In my enviroment I fixed this issue by turning on the remote registry in windows 7. MBSA scanned just fine on my test group after starting the service.
Might be a good idea to turn it off after you get done scanning. You can control services with the "sc" command in a script or use group policy to set its start state (auto,manual,disabled). I havent dug deep enough to see if you can start the service with
gpo.
