This is similar to the issue this user is having:
I have Exchange 2003 running on a Single Server (not a DC) I have 2 DC's one is a 2003 Server, the other is a 2008 R2 Server.
We are migrating from Exchange 2003 to Office 365. Using the TES tool, I am getting the The RPC_S_SERVER_UNAVAILABLE error (0x6ba) was thrown by the RPC Runtime process. error.
I have searched the internet...did the registry change for the ports on Exchange and the port on the DC's. No firewall on the servers, even uninstalled and reinstalled the RPC components on Exchange and same errors.
Here are some links to things I tried (and did not resolve)
I am stuck....I searched the rest of Experts Exchange also, I found similar issues, but those didn't fix my error either.
Thanks in advance