it looks like you are using the same port for hfs as the router login page you router is either a linksys or netgear to the sounds of it. the issue you are experience is that the router from you external ip which is what you freedns is directing to is connecting to the router as the router has been set up to be configured from the external ip, port forawrding to another port or diable remote rouoter configurations. More detail may be need to help you in this issue as 1 i don't know the router you have which may be different, 2 i don't know what your have your prts as, by default linksys and netgear use port 8080 and some times port 80 for there remoter/external ip configuration...
also, due to thte ttl and other values, using HFS serve test port can and sometimes will fail, as long as you have set you dns name to the router/hfs and have hfs set to the port you want with the port forwared to the router, you should be able to acess you hfs form you external ip adress
need to know you external ip adress, it is:
http://www.ipchicken.com/