Donald,
Yes, being on a different subnet is probably the issue. Design and Workflow needs to be on the same subnet, or they won't be able to see each others.
If they are on the same subnet, it should work. Make sure the PlanetPress Messenger service is active on both the Design and the Watch machine.
If you cannot use the computers on the same subnet, you can click on "Save PTK file", and manually copy the file to C:\Documents and Settings\All Users\Application Data\Objectif Lune\PlanetPress Suite 7\PlanetPress Watch\Documents on the Workflow machine. This is the manual way to compile the form.
Regards,
Rapha