Windows Security service is stopped

I have a problem with Windows Security (thanks to Event Viewer for
information). Whenever I start or restart my PC and an hour passes, the
Windows Security service stops by itself. When this happens, my Norton
AntiVirus 2003 program and the Windows Firewall service are disabled and I
have to turn enable them manually.

I did use every protection program to scan for viruses, trojans, and
spyware. The result is that Spybot detected a registry key change in
AntiVirusDisableNotify and it was fixed by changing the "1" binary number to
a "0". A week later, however, I ran Spybot and that registry key was changed
again and I fixed it again. I looked into Event Viewer to find the source of
the problem. This website doesn't have information to fix this problem, so
here's the source of the problem:

ID: 1801
File name: xpsp2res.dll

I am running this PC with the latest service pack as well as having the
latest OS updates installed.