Strange network behavior

[Weaseal]

I got a new wireless router recently and I am experiencing some strange behavior. We have a network of about 15 computers spread over a few switches. All of the computers use DHCP to receive their addresses from the router, and successfully connect to the internet and one another.

The odd behavior is that I am unable to log in to the router's web interface from all but one computer. Clearly all computers can access it in some means, because they use it as a gateway to the internet and receive their DHCP information from it. Ping and tracert work fine to its address. I have double and triple checked that it has no filter as to which IPs can access its web interface.

It's a D-Link wireless ADSL router.

I'm going nuts!