Dear Friend,
Either the credentials you are providing are incorrect or Check with your firewall expert. They open the firewall for PROD servers so there is no need to use the Proxy.
OR
You have to set the Credentials in two locations to get past the 407 error:
HttpWebRequest webRequest = WebRequest.Create(uirTradeStream) as HttpWebRequest;
webRequest.Proxy = WebRequest.DefaultWebProxy;
webRequest.Credentials = new NetworkCredential("user", "password", "domain");
webRequest.Proxy.Credentials = new NetworkCredential("user", "password", "domain")
If the above things don't work out then follow the link
http://blogs.msdn.com/b/jpsanders/archive/2009/03/24/httpwebrequest-webexcepton-the-remote-server-returned-an-error-407-proxy-authentication-required.aspx[
^]
Don't forget to mark this as your answer if it helps you out.
Thanks