My gut tells me it's something to do with Norton Antivirus ....
Trays are usually empty when I shutdown.
I wouldn't be surprised if a MS security update screwed my computer. But, the awful part is, if I want to 'back track' and/or uninstall these updates, I'm essentially screwed unless I'm willing to reinstall applications which were 'affected' by the security updates (as it lists for you when you try uninstalling them).
Fantastic links. I've visited the first link several times before and tried everything there that relates to this problem. No luck so far. Looking at the other link now.
Dr. Watson 1.00b: "No Faults Detected"
msconfig (XP SP2): I check it religiously. I always strip down the loading apps & services to a minimum.
task manager: I also check this frequently and haven't noticed anything 'unusual' running just before shutdown.
Other ... recently virus & adware scanned, which came up clean.