Sharing access problem

We are still having this problem. We thought it was Robocopy,
and some of it may have been, but a fundamental problem still
persists. It started with the installation of SP1 for Vista.

Two Vista computers, a desktop where the files are kept,
and a laptop where word processing is often done
using Word Perfect X3. About once a day Word Perfect,
Word and Excel have the same problem, on the laptop will
not be able to access the shared folder on the desktop via the
network.Since the laptop can access the Internet it is not a network
problem. There is no indication in the event logs that anything
was wrong and all services and processes look normal.
Maybe half of the time the desktop will have reduced the amount
of memory in use to under 500MB (unusual). 100% of the time
the desktop will stop during the reboot at the "Shutting down"
screen and we have to power it off manually. It will then boot Ok.
After the reboot the laptop can again access the shared folder.

While it repeats, we have not found anything that allows us to
force a repeat. Without any way to deliberately replicate the
problem, troubleshooting is proving difficult.

Microsoft's last suggestion was to uninstall the antivirus
software and see if that helps. Since we have gone as long
as 2 days between repeats and we do a lot of surfing, I am
really not very interested in leaving my computer unprotected
for that long. The shortest amount of time between repeats has
been about an hour.

Does anyone have any ideas? This problem is really really
annoying.

Thanks!!