Are you getting any popup messages from McAfee warning you about Trojans being blocked? If "yes" you may need to contact the McAfee Virus Removal team. If you are not receiving popup messages about Trojans being blocked then take a look at this document on how to remove and reinstall the McAfee program using their removal tool.
I had the same problem after a update and was told by the McAfee Support Team member I should use the above MCPR.exe (link to download the tool is found in the above document) to remove my McAfee Security Center and then reinstall the product from my online McAfee account. The above method did worked for me.