Windows Server 2003 uses secure encryption which the version of samba in Panther (Mac Operating System) doesn't support. The server's authentication needs to be changed to allow unsigned authentication, per the following: On the server, go to "Start" ->"Administrative Tools" -> "Domain Controller Policy" (not Domain Policy) and look for "Security Settings" -> "Local Policies" -> "Security Options" -> "Microsoft network server: Digitally sign communications (always)". It should show "Enabled" by default. Double-click on it and set to "Disabled". Then close the app and reboot the server.