Windows Defender Shutting Down

I have been having a problem with Defender shutting down often. Seemingly
it started when I updated to the regular public release, I was using the
Beta and this problem never occurred.

I have uninstalled Defender and reinstalled it according to MS procedure
without correcting the shutdown problem. I have looked at the only KB item
and follow the pertinent items in there, I think? That gave me a days
improvement by it not shutting down. the next day it was shutdown.
Sometimes the icon shows there is a problem sometimes the icon disappears.
It worries me because I do not get an immediate warning, I have to be aware
to check the status most of the time. I have not called MS support yet. I
run Registry Mechanic at reasonable intervals and have OneCare to tune up
once a week. I am running an AMD Athlon Manchester, Socket 939, Dual Core
processor on an Asus A*N32 Sli Deluxe MOB which has not exhibited any
problems since I assembled it in 2006 July. I do not suspect equipment has
anything to do with the problem but thought I would supply the info.

I am using IE7 and WinXP have automatic updates for the MS and Office. I am
running the latest version of OneCare also. I have wondered if there is a
conflict between Defender and OneCare since it seems some features are
duplicated or nearly so.

Will someone give me some advice or at least confirm that I am not the only
person in the world having this problem? Thanks Al