There shouldn't be a problem as long as McAfee is the only security software that is active, have you any other installed?
I have both Vista SP2 and Win 7 SP1 x64 machines and they are fine following the latest updates from both Microsoft and Mcafee.
It could be that your installation has somehow become corrupted. This can happen for a number of reasons, infections, use of registry cleaners, frequent use of System Restore etc just to name a few.
Assuming this is about the home products I suggest you try the following:
Uninstall McAfee via Control Panel/Prorams/Uninstall a Program
Then run the McAfee cleanup tool listed under Useful Links at the top of this page (MCPR)
Reboot and reinstall your software from your online account.
This is precisley what I've done. Uninstalled, ran the cleanup tool, reinstalled, SAME ISSUE.
Not sure where to go from here....
Are you running any other security software?
Technical Support Online Chat might be able to troubleshoot this by linking up to your machine.