The “unauthenticated network” in Vista, which means RDP and many other things do not work (basically, it has broke kerberos) was in my case due to two computers having the same name.

I have no idea why I was allowed to join a Windows 7 laptop called Julian-PC to the domain when there was already a Vista desktop called Julian-PC on the domain.

There were no warnings of duplicate names on the network, but adding a new computer to the domain with the same name as an existing computer caused the existing computer’s Computer/Machine Account to be overwritten in active directory, and so the machine was no longer a working domain member and kerberos/authentication was broken. We were seeing “cds.local 2: unauthenticated network” instead of just “cds.local”.

Hope this helps others.