Mac Pro Server Firewall

Mac OS X 10.7.5

Mac Pro Server Mid 2010

My server's firewall is up and running and the office's client computers (iMacs and MacBook Airs) can communicate with the server (e.g. share screen works both ways).

The trouble is I have an app on the clients that can't access the same app on the server. The app on the clients say I may need to open port 1234 on the server. I did that thusly:

sudo ipfw add 1000 allow tcp from any to any dst-port 1234

and I confirmed the port is open via Network Utility's port scan. Still can't access the app on the server.

Suggestions?