Sharing 'Favorites' , Email Store folder across XP pro network fails sometimes

[Al]

I have 3 computers running XP pro, all sharing files successfully.
One of the computers is acting as a file server for the other two,
and all the computers have the same set of users. I'm also running
Norton Internet security on these computers.

I changed the favorites directories (also email and my documents) to be on
a shared drive on the server PC (i.e. Z:\Al\Favorites). Most of the time
this
works great - I can access the same set of favorites from any PC.

However, randomly this gets reset back to the default directories. When I
look with
windows explorer, the mapped drive (Z:) has a red slash through it, even
though
I can access files using windows explorer without any difficulty. It appears
as though any
program other than windows explorer gets an error when accessing the mapped
drive.

I also have similar problems with Outlook express 'losing' the shared store
folder.

To solve the problem, I simply log off and log back on. The red slash is
gone,
but I need to reset various registry settings to get back my shared
settings.

What does the red slash mean?
What could cause this?
Is there any way to prevent Internet Explorer and Outlook Express from
resetting
the directories back to the default when an error occurs?

Thanks for any information.

Al Lehmann