Logon unsuccessful

I have a 2003 Network. I am having some problem when my users are
connecting using their VPN client. (WINXP, Securemote). First they
logon to the domain using cached information and then they activate
the VPN client.

Outlook is working just fine but when they try to map network shares
they get the following.

Logon Unsuccessful:

"The User name you typed in is the same as the user name you logged in
with. That user name has already been tried. A domain controller
cannot be found to verify that user name"

It works if you use a different username when you map the drives.

Kristian