Nion communications across a router

Hi

We have installed a system with 3 Nions connecetd via XDAB in one location and a single unit in another location.
The 3 units and the monitoring PC are all on one sub net & the remote NION is on a different sub net.
We have set up pandad on the PC so we can deploy to all NIONs - they are all using the same project file & this works fine.
We are connecting to one of the local Nions via Telnet to change parameters on the NIONs in the XDAB cluster and this works with no problems.

We now would like to change parameters on the remote NION as well via the same Telnet connection, they appear to be changed when we set them, but the actual status of the controls does not change.
I suspect that this has something to do with the IP routing but am not sure what we should be looking for.
Is there a set up in the NIONs themselves similar to the pandad configuration that enables them to "see" each other?

We were able to connect via Telnet directly to the remote NION & change settings but this is not a practical long term solution.
However after messing about a bit to try get something to work, we now are getting the following message in the Net ctl RATC2 status window "could not start because'open failed:Address already in use' "
What address is this refering to?

I have tried using the project linking devices on the same site to connect to another project, also on a different sub net, but they also do not work!

Help!