Sometimes you can get the following error:

The RPC server is unavailable. (Exception from HRESULT: 0x800706BA).

This means that either your RPC service is not working correctly (rare but happened to me), or that your RPC packets are blocked by a firewall.

Possible solutions

• Try the Test-NetConnection cmdlet to check if the port 135 is open.
  (Alternatively, you can use the telnet client)

Test-NetConnection -ComputerName MyComputer -Port 135

• Check all your firewalls’ (network, computer, antivirus) logs to see if the protocol is blocked
• Restart the remote computer to be sure all RPC services are working fine

A tricky case

I came to another case where the client computer had a DNS record but not the one matching to the Full Computer Name.

For remembrance: Full Computer Name = Computer Name + Active Directory Domain Name

For example, you have registered MyComputer.MyCompany.Com but you have not registered MyComputer.MyADDomain.MyCompany.Com

This can happen in companies where computers have aliases for their computers and the computer does not or cannot register the DNS name itself.

In my case,  as soon as this record was added to the DNS, my SCOM agent had did not return the RPC error anymore.

More about

How RPC works (Technet)