Moodle networking (MNet)

I'm getting the following error message when I try network two moodle installs.

RPC auth/mnet/user_authorise:XML Parse error in payload: syntax error At line number: 1 Which reads: ERROR 3:3:XML Parse error in payload: syntax error At line number: 1

Any idea's?

Here is some background. They are both on the same server with the same domain name.

They previously worked until we moved them to a new server.