"You can also start Task Manager when you have the popup from "unload" to see what programs/processes are running to try and identify where "unload" comes from."
I just had the poster's issue, after re-enabling IIS snap-in in the Windows Component options."
Quit the window, inserted my XP Professional SP2 CD, no help.
Task Manager with CPU usage as filter, showed EEventManager.exe and sysocmgr.exe reappearing.
sysocmgr.exe is the Windows Component Manager of course.
EEventManager.exe is the Epson scanner Event Manager.
That one Epson process is loaded at startup, the CPU filter indicates it was in use off and on as the "upload" popup appeared and was canceled.
Quitting that one process in Task Manager allowed the Windows changes to finish.