R50L - "Server name list is not valid" when changing RDP port

I'm just trying to set up a basic RDP connecion to a remote session on a Windows 2010 server. I've only ever used the RDP connections on the ThinOS clients, never the Linux clients. Is there something I need to do, or change, other than the server in the RDP configuration tool?

Code:
Server: 12.34.56.78:1066

Any help would be appreciated.