forwarding ports will not help.
your router does NATP, which means when it sees PORT command with any ip address, it always changes that ip to YOUR ip. it is useful for regular downloads, but completly destroys ability to FXP.
the reason why it other ports work is becuase your router only monitor port 21 for ftp commands, not other.
getting new router will help(as long as it doesn't do the same thing).
or you could just buy flashfxp and have access to latest betas
