That's real odd. I stopped one of the clients, edited the config file from port 7773 to 7771, saved the file and restarted the client sometime over the weekend.
It's the same client that was working up to that point on the other port. I'll try a different port when I get near the box again in a few hours.
I have two copies of the client running on a dual core box, each client from it's own folder.
Edit: I changed the offending client to 7772 and it's working fine.