There are two ways of curing this that I know of - although my experience with this is XP not Vista.

1/
On one PC, I had a similar/same message. This turned out to be a registry problem which could only be solved by a restore point (which I didn't trust) or using the Windows CD to update the Windows already installed. Then it returned to a state of grace. I have no idea what caused this glitch. The AV program (not McAfee remained usable).

2/
On the other PC, I lost some functionality with McAfee messages to that effect. I forced a McAfee update and the orblem went away.

Let us know.

Follow all the steps given HERE, with the exception of Deckard Scanner instructions. That program is no longer available.
Substiture instead a full system scan with HiJackThis.
Post back here with all requested logs. DO allow all programs run to clean or remove all items found.

Thank You!
system restore worked for me.....restored to a point before some Windows update .... Now its as good as before...
Thanks!

Well done. Please mark this thread as solved.