I have experienced a similar (not exactly the same) problem. Intermittently, the warning box ("not protected") pops up, and, usually, the problem is "system guards". Occasionally, the problems occur with spyware checks. Upon clicking "Fix", the problem(s) is/are usually resolved.
After some investigation, it seems that if any intermittent performance problems with one's ISP (or the router, or wireless service) can cause the failure of subscription verification. I have noted that if the ISP service (or router) is totally down, the "System Guards" failure doe not occur.
One additional observation as to the "System Guards". I have found that all of McAfee's Windows "Services" are automatic starts EXCEPT for "McSysmon" (surprise: the service named "McAfee System Guards" !), which is set to "manual" start. Is this the correct setting ? If so, a delay in the manual start of the "McSysmon" service might give rise to a false indication.
EDIT: I note that a similar problem is in the "Virus Scan 12" sub-forum.
getting my tin hat ...........