Error - Cannot contact site at the specified URL. There is no Web named "*.asmx"

The problem you are having is that your site path is not specified correctly.

instead of

string siteUrl = @"http://servername/sites/subfolder/default.aspx";

try

string siteUrl = @"http://servername/";

if that doesnt work, use whatever address you can enter into your browser of choice to get the site to load.