What versions of Security centre and virusscan are you on?
It has most suggestions
I really feel the install got corrupted so follow the suggestions in the FAQ leaving a reinstall as last thought .
If issue still persists, please contact technical support chat from this link http://service.mcafee.com/TechSupportHome.aspx?lc=1033&sg=TS and they will remote in for further diagnosis
The security features included within your suite could get disabled if there yet another active virus scanner that is having a conflict between them or if the base operating system in not stable .
Could you please let us know some of the below details to get this straightened out .;
What is the operating system installed ?
Did you have / Do you currently have any other security software in the PC ?
Please run MVT from here : http://mvt.mcafee.com and let us know the status post that along with your session id number.