Don’t ask me why, I just know what I did to work around it.
I was engaged in establishing a database mirror for a new monitoring database for an established Lync 2013 CU4 EE pool. When it came time to publish the topology and install the new databases, the mirror refused to instantiate with an error of:
An error occurred: "System.Runtime.InteropServices.COMException" "The RPC server is unavailable. (Exception from HRESULT: 0x800706BA
Lovely, eh wot?
The SQL server version for all three servers in question is SQL 2012 SP1. I went through the usual routine of checking the services, the firewall rules, the rights and permissions on the SQL primary, mirror, and FSW. All of that looked as it should. Here is a good outline for you to follow should you need it.
What fixed it for me? We turned off the firewall for all interfaces on all three SQL servers. I know, but don’t ask me. After the successful mirror activity, we turned the firewalls back on for all interfaces on all three SQL servers and everything seems to be happy.