A write operation was attempted to a volume...reboot

XP is continually rebooting after installation of SP3.

I get to the Windows screen, then usual blank screen, then black screen with cursor, then error = "A write operation was attempted to a volume
after it was dismounted," then boot back to post.

Same problem in all safe mode options.

Tried: chkdisk, memtest with no problems.

It is not an AMD processor.

It will boot from a cd and run under load until I stop it.

Any other ideas? This is for a client who has many apps installed, so I am reluctant to do a repair install.

 

Have you thought about a non-destructive repair?
Read this before attempting.

http://www.freerepublic.com/focus/f-chat/1664082/posts

 

I would see if you can access system restore in some fashion, perhaps from the Windows CD if at all possible.

Otherwise, yeah a nondestructive repair may be your best bet.