Have you tried opening the McAfee Virus Scan Enterprise console and verifying if all is fine or not ?
It may also happen the Windows Secuirty Centre is not able too properly monitor the AV status on the concerned machines and thus it displayes that error message. Please check if the VSE console hows that all components are running or not.
Also, you can open up the task manager and seee if all the McAfeee processes are running.
Please revert for any more information/clarification.
Frm yesterday night i m unable to turn on virus protection to my sys.In windows security centre i clicked in check box to turn on my virus protection though it is showing to turn it on again.even i m unable to scan my sys thru my mcafee antivirus plus which i m using...PFA screen shot