I'm trying to setup remote access for my linksys 3200 so that I can configure it through the WAN port. I have turned on remote access, however when I try to connect I get a 404 error. The settings I have are:

When I try to access xxx.xxx.xxx.xxx:9999 I just get a 404 error. I have allowed RDP access to a computer behind the router and this works fine on the same IP address. Any idea's on what else I have to do to allow remote management access?

UPDATE: I tried changing the port to 80 and it works. Change it back to any other number and it doesn't work. Modem is setup with a DMZ to the router's IP. Why does it only work on port 80? BTW I can't use port 80 because there is a website hosted behind the router.