Network gets flakey after overnight scan

On XP Home machine, recently updated but no SP2. On a
simple corporate network with a few dozen machines.
Machine has been stable for many months.

I installed AntiSpyware and ran a scan manually and it
found nothing. Left it to run nightly at 2AM.

Came in next morning and the "network is broken" icon was
there in my sys tray. Everything seemed OK. Rebooted and
the icon went away.

Came in NEXT morning. Email is not working and internet
access hangs. Rebooted. Everything is OK.

I strongly suspect the overnight scan is messing with the
network connection.