i found that my ftp client allows me to use two fxp types, one being passive which wont work with my router and the other is called "port method" no idea how that one works at all. all i know is it does work for me
with flashfxp i had to add the site(s) to the fav list, edit them and there is an option somewhere for what fxp method should be used, selected the "port" one and recconect, all should be good.
or you could try forwarding the passvie port range to your lan ip but that would have taken time and i am lazy.
hope that helped