Parental Control: Timelimt doesn't work anymore after upgr. to OSX 10.6


After the Upgrade from 10.6.8 to 10.8 on machine 1 and from 10.7.4 from machine 2 to 10.8 on both machines the time limitation doesn't work anymore.
What I dit until now:
- New account without admin rights with parentalcontrol
- deleting all the rights and reinstall OSX 10.8 over the existing system (this was the hint from Appel)
Until now - no chance.
Does anyone now about this problem? A solution?

Regards, Martin