be sure you have Short GI Relay off...
and by the way...
you are having WAY too much radio interference in your place. it doesn't matter how much encryption you put on the radios they are beginning to communicate with each other and that is what is locking up the DGL-4500. eventually i'll put up a diagram of how my network is set up, but i recommend you get off of that slow wireless internet gateway. and get a real internet through cable :-D
having that many Wireless routers is a nice thing though, since the DGL-4500 only handles up to 3 wireless clients decently, but having them that close will only create cross communication and lock up the DGL-4500, however, if you put one on G and one on N you might be able to survive, but all this extra RF interference is going to drown out the Wireless Gateways connection. its like using a bunch of high pitched noises in a kitchen to speak privately in presence of a spy's mic, it will only pick up the static noise, and you can easily speak to your friend, but at close proximity. what you got going on is your ISP is the spy's mic, and your routers are the high pitched noises. disable all internet radios and try that out.