Network Permission Problem

[Gerry Doris]

I have a small network with several boxes running either XP or FC3.
Until recently I've been able to access any box from any other box.
However, something has changed.

On my main Linux desktop when running as a normal user I receive a
message that I'm unable to access an XP share because I don't have the
necessary permissions.  This only occurs when trying to access this
specific XP box from this one Linux box.  Access to all other boxes
works fine.  I can always access this XP box if I'm running as root.  

The problem is occurring when as a regular user I click on the
"Computer" icon in the top left corner of the screen.  I first see a
list of all boxes on the network.  When I try and open the problem XP
box I get the permission error.  I can open any other box whether XP or
Linux.

When running as root I can either use the command line mount command
successfully or click on the "Computer" icon.

How could I have lost permission for just this one share as a normal
user?