Suddenly, none of my computers on the domain can access the network shares or shared printers from my SBS 2003 domain controller. The permissions are still good, all services are fine, no errors on server. Even when logged into a workstation as the domain admin, I get "The operation being requested was not performed because the user has not been authenticated" when trying to access the server shares via its UNC path.
Workstations are Win7, up to date. SBS 2003 server is up-to-date.