I am having the same problem as the original poster. I have performed the steps identified above to no avail.
I have a linux centos virtual server on my network where I have setup a very simple website (like 1-2 liner) that I have setup for testing the server configuration. It was working fine in early january and then all of a sudden, one day it stopped working. I don't remember if it coincided with me turning on the Advanced Security, it might have; but since then, I cannot get to the site from outside. This is not a public or commercial server. It is solely for my purposes - very low traffic and not on all of the time.
I have been unable to get my port forwarding to work again. Customer support was no help. I am about to use this darn gateway as a pass-through and put my own router and DNS server on it!