I couldn't get it to work either until today when I downloaded a free program called Port Map which makes it so easy to map UDP 5198 and 5199, and now Echomac works just fine.
Hope it works for you.
Just download Port map and open it.
Click on the + mark, check off the UDP box and type in port 5198.
Repeat the process typing in port 5199.
I had previously tried using Airport utility to open up Airport's ports and just didn't have any luck.
Best of luck.