Problem logging on to network share

I admin a network with 10 workstations and 2 servers. We just upgraded 2
workstations to Vista 64. These workstations connect to a server running
Server 2003. I finally got the yVista machines to connect to the Server,
after much hair pulling, but we still have a proble.

I setup a shared folder on the server that both machines access. One logs in
at domain admin level, the other at user. When they access the folder for the
first time after a reboot, they have to login to access it with a blank
password.

If they use their correct password, they cannot access the folder.

Any ideas?

Regards,
Rustyc