XP Pro SP3 - Shutdown Hangs - Shell Extension

My system has for some time failed to shutdown without asking to to "end now"
for a program that is only listed as "System Shell Extension."

How do I find out what this is and "put it to rest?"

Nothing shows in system log, and there are no other symptoms. No drivers
that show issues, nothing that malfunctions. The only symptom is that I need
to wait as the machine shuts down to tell it to "end now" or "cancel" so that
the machine will shutdown.

BTW - the software install forced reboot does not have this issue but my
selection of a reboot from the shutdown still encounters this.

Sure could use a hint as to how to find or resolve...

Thanks much!