Map Drive Problem VPN

I have two domains each with a single PDC running Server 2003 with ISA
running as proxy and firewall.

If I make a VPN connection from the PDC from domain A to domain B, I can map
drives to shares on domain B no problem.

However any other computer on domain A will let me make a VPN connection to
domain B (I can even run remote desktop to domain B), but I cannot map to
any of the shares.

I get an error 5 access denied message.

I allow anyone with full share permission, and tried opening up both ISAs to
allow total connectivity with no change in effect.
I looked at the event manager on all the machines and haven't really gotten
any clue of the problem.

BTW if I use my laptop (not a member of any domain) from a third location
it works fine.

Can anyone give me a idea of where to look?