Mac Freezing after waking from sleep

Hi, Please could someone help
everytime I allow my Mac to sleep with Parallels 6 running windows 7, following a wakeup my mac freezes requiring a hard reset .
Often this will cause the mac not to recognize the hard disk forcing me to start from my backup. This happens everytime the mac goes to sleep with parallels running. I have tried re installing my mac OS 10.6 , tried repairing disk permissions , tried reinstalling Parallels 6 tried re installing windows 7 . Nothing seems to help > I never had this issue with parallels 5 . Really regret upgrading , quite honestly it would be easier to simply use my PC for the programs that require windows
But any help would be gratefully received
regards