Today I had some problem of connecting to some of Windows 7 machines. The error I recieved was: The RPC server is unavailable.
After searching some articles on the net, I found out that I need to enable RemoteAdmin firewall rule, and add DCOM TCP port 135 to Inbound rules.
call netsh firewall set service RemoteAdmin enable
call netsh firewall add portopening protocol=tcp port=135 name=DCOM_TCP135
For port 135 there is a firewall rule Windows Management Instrumentation (DCOM-In) which needs to be enabled.