Got the above error when consuming a Web Service from a Windows Application written in .Net 1.1.

Many sites quote proxy server issues etc but one quick thing to check is I forgot to change the reference setting of the Web Service to Dynamic. It was set on Static and when the Windows app was calling the Web Service it was looking for it on localhost.

Changed it to Dynamic and checked the value in my app.config file and the error was gone.

Worth checking first.