If you see The RPC server is unavailable. (Exception from HRESULT: 0x800706BA) error message then it could mean that either your RPC service is not working properly or that your RPC packets are blocked by firewall.
Restart the Remote computer
Run the following command to check if your Port 15 is open - Test-NetConnection -ComputerName MyComputer -Port 135
Ensure that all the RPC Services are working OK
Check your Firewall settings and logs and see if thr protocol is being blocked.