Windows DCDiag Generating - Error 0x6ba "The RPC server is unavailable."
Once you arrive to Windows 2008 with Advanced Firewall and you run DCDiag you could end up with "error 0x6ba The RPC server is unavailable." This is the result of the remote DC not allowing RPC connections from the firewall being enabled.
To remove this error and allow DCDiag to be run remotely, open up the following rule on the remote DC's Firewall settings:
Remote Service Management (RPC)
To not open this up to widely, I configure the "Scope" tab to only those ip addresses that will be running DCDiag remotely