The network location cannot be reached

I have a client (Doug) who has Windows XP Pro installed on his laptop and
logs into our Windows 2003 domain. He has a folder on his laptop shared as
"\\doug\bidding", which he and 2 other employees access. The 2 employees also
have laptops and the 3 of them travel to bid lettings. They connect their
laptops together via a D-link DI-604 router when on the road.

Everything has worked fine since we set this up about 9 months ago. Their
last bid letting was about a month ago and it worked then. However, when
they went to a letting on Monday, everything fell to pieces and I have been
pulling my hair out trying to figure out what has changed and why. Everything
still works correctly in the office, just not when on the road and connected
through the D-link.

If the two employees log in using their cached domain IDs, they get an error
saying "no logon server could be reached" when they try to access the share.
If they log in as local users on their laptops, they access the share without
problem, but email etc is wrong since they are using different profiles.

Now for the pulling hair part. When not in the office and logged into the
domain, Doug cannot access the share on his laptop whether he logs in using
his domain ID or as a local administrator. He gets the error message "The
network location cannot be reached. For information about network
troubleshooting, see Windows Help." He gets this error message whether he
tries to access "\\Doug\bidding" or just browses to "\\Doug". However, he can
access email and browse the internet through the D-link so I am confident
that TCP/IP is fully operational. And as I said, the other 2 employees can
connect to his laptop if they log in as local users.

Does anyone have any ideas on why he suddenly can't access the share on his
system when not connected to the domain? Also, why are the other users
suddenly receiving the "no logon server..." error?

Mezlo