The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
If you get this error message [ The RPC server is unavailable. (Exception from HRESULT: 0x800706BA) ] when you are trying to work with Reports on a remote server this post can help you.
You could also see an error message saying that : “Cannot create a connection to data source ‘MyDataSource’“.
In my case I saw both error messages in Report Server log files. You can access these log files by following D:\Program Files\Microsoft SQL Server\MSRS11.MSSQLSERVER\Reporting Services\LogFiles path.
According to this post on stackoverflow this may be caused by a firewall issue.
I do not know what the exact problem is but restarting report service resolved my problem.
You can do it by opening Reporting Services Configuration Manager and stop Current Report Server and start it again.
Hope this helps!