Offline files cannot synchronize - Invisibl

I'm desperate now.
I have a recurrent problem with my offline files since I upgraded to vista.
Any file I create/modify while I'm offline generates a sync error "The system
cannot find the file specified".

Vista is the Client; the server is an XP-Pro. This setting has been working
flawless for over 6 months until the update.

During the last 2 weeks I have checked everything I can image, including
resetting the CSC database in Vista (that took some time to find!), EFS keys
perfect matching (including recovery agents.. ), rebooting both machines
uncountable times, and applying a special hotfix for XP (KB903891). To not
avail.

A bizarre symptom is that those new files are actually available (in Vista)
while the drive is online, and I can make copies of them to the very same
directory where they were originally created. These copies then appear in
both machines, synchronizing flawless (while the originals remain in error).

I also created new shares, and new synchronizations, and enabled/disabled
off-line files settings (with reboots several times….)
Any ideas ?