I don't know what exactly is going on. What are the errors ? It may be a bad DAT push.
The easiest solotion, IF it works:http://forums.mcafeehelp.com/showthread.php?t=229135
The alternatives are a chat with technical support of McAfee, or uninstalling and reinstalling McAfee. In the latter case, it's best to use the MCPR tool and follow the instructions that can be found elsewhere on this forum.
Of course, it's possible that the problem is caused by malware, in which case you could try scanning with the free MBAM and SAS.