Vista - Vista/XPPro problem

I have two desktop computers networked using D-Link 624. The main computer
is on Vista and is hard wired to the router. The secondary computer is on
XP-Pro and is wirelessly connected. From the XP computer I can access and
open all shared folders on the Vista computer. However, from the Vista
computer I cannot open or access any of the folders or files on the Vista
computer. I have done a lot of experimentation even to the extend of not
loading the anti-virus software and turning off the Windows firewall. It
did not help. The shared XP folders show up on the Vista but when I click
on any of them I get the dreaded "not accessible, not enough server storage
is available to process this command". I have already increased the
IRPStackSize to 21 decimal on both machines but that did not help either. I
am now at a loss as to what else to look at or where to go. Comments and
suggestions via the newsgroup are welcome.