Remote desktop connection netgear adsl

I have 2 adsl routers one is an older Dlink 504 and another router which is a netgear DG834G(v2) with the latest firmware (version 4)

The problem I am having is that whenever I use remote desktop connection over the lan with the dlink it works perfectly. Then when I plug in the netgear router, I can connect (authorised, using the desktop, etc) for about 20 seconds and then it locks up and eventually just fails and errors out with the error message “network problems have caused this connection to disconnect…..”

I’m pretty sure that the firewall doesn’t affect lan traffic on this model, but if we solve the lan problem I am assuming the wan will fall into place