I'm having difficulty with the pc outlined in red with the asterisk in the diagram. When trying to log on to domain A with an uncached user I get the domain is unavailable error. If I log on as the domain administrator (cached locally) and authenticate against the DC (W2K8) and log off, other users can then log on to the domain on that PC successfully. Prior to authentication the DC does not respond to a ping, however the file server on the same subnet does respond. The netdiag results showed dc discovery and dc list as passed with domain administrator authentication and failed with no authentication. When I log on with a cached user the PC can't communicate with the DC, and fails dc tests in NetDiag until I authenticate against c$ on the DC. Please let me know if you have questions regarding the environment or my poor diagramming. I'm probably missing important detail.