问远程服务器返回错误：(403)禁止。错误

EN

     string str= TextBox1.Text;
     var request = (HttpWebRequest)WebRequest.Create("https://www.google.com/cloudprint/search?output=json&clientid=" + str);
     request.Method = "POST";
      SetupWebRequest (request);
      string postData = "This is a test that posts this string to a Web server.";
      byte[] byteArray = Encoding.UTF8.GetBytes (postData);
      request.ContentType = "application/x-www-form-urlencoded";
     request.ContentLength = byteArray.Length;
     Stream dataStream = request.GetRequestStream();
     // Write the data to the request stream.
     dataStream.Write(byteArray, 0, byteArray.Length);
     // Close the Stream object.
     dataStream.Close();
     WebResponse response = request.GetResponse ();