No such host is known message when working on a LAN

I am trying to connect to a website I work on from a LAN and receive the no such host is known, connection closed message when I know the host internet site exists. If I connect using a dial-up connection, all works fine but I continually get this host unknown message when I try and connect via a LAN. Any ideas why I am getting this message? I've checked all the settings and not found anything relevant.

Thanks!

Your LAN probably has a proxy server and/or a firewall.
D