TigerShark,

I've only seen a problem like this with PC Anywhere installed/running but it was after an upgrading a system to XP Home a few years ago and ended up removing PC Anywhere.

I know you've filed it away in the file with the label that wraps around the file twice but in case you have an urge to dig into this again ...

Have you tried to have them restore to a point prior to this latest corruption? Were there any errors listed in the eventsviewer if you got in this time?

Since it has happened on several occasions, maybe have them create a backup SAM once everything is back to "normal".

I did see this article which may be of use:
http://support.microsoft.com/default...b;en-us;312131

This isn't directly related to the issue but may provide some further options to investigate as your time permits:
http://support.microsoft.com/default...;en-us;q307545