Hi...
Please add some more information like any major changes done on the computer recently including a system restore or installing any applications etc.
If nothing has been done, then proceed with re-installation of McAfee.
Please make sure to use the MCPR tool after removing McAfee from Add/Remove programs.
http://download.mcafee.com/products/licensed/cust_support_patches/MCPR.exe
If issue persists after re-installation, I will suggest that you contact the McAfee Technical Support. Free phone and chat supports are available..
http://service.mcafee.com/TechSupportHome.aspx?lc=1033&sg=TS