So a few days ago I changed the GPO (Group Policies) on the domain controller to setup our SMB network for unencrypted communication so that clients like Mac and Linux could get on SMB with the windows machine. Well these changes slowly propagated out to all the machines — only for me to find that Win2K3 ignores it completly. All the XP/2k machines could interact, but they could not interact with the 2K3 machines. For some reason 2k3 must have encrpyted communication — reglardless of the GPO (because I double checked the security settings and they all matched).
I went back to the DC, changed the GPO to allow encryption and and signing if avaiable and suddenly all the machines can talk again.
God I hate windows.