I have the same issue, as an eariler thread, but on the ZENworks server (10.1.0), I have tried all that has been suggested, but the "zac unr -f" won't work as it states that it can't be run on a primary svr, so I haven't tried the newSID option. All the other devices (agents) appear to access the Primary Svr ok, it just the agent on the svr that doesn't.

the local log, shows this

[DEBUG] [02/06/2009 18:40:27.656] [1232] [ZenworksWindowsService] [8] [] [ZenService] [] [Registering device] [] []
[DEBUG] [02/06/2009 18:40:27.687] [1232] [ZenworksWindowsService] [8] [] [RegistrationManager] [] [Error during device registration: Unexpected server result. Server code: -34. Server message Invalid Device Authentication Information.] [] []
[DEBUG] [02/06/2009 18:40:27.687] [1232] [ZenworksWindowsService] [8] [] [RegistrationManager] [] [Unable to update device status with any service]

suggests very welcome,