"{"errcode":41008,"errmsg":"missing code, hints: [ req_id: ginCi5yFe-.rOgNA ]"}" 上面这是后台返回给前台的这是怎末回事？求各位大神详解!!! 下面是后台代码  用的vs2013和c#

  public void GetCode(string code)
        {

            string serviceAddress =
                "https://api.weixin.qq.com/sns/jscode2session?appid=我的&secret=我的"
                 + "&js_code=" + code + "&grant_type=authorization_code";
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(serviceAddress);
            request.Method = "GET";
            request.ContentType = "text/html;charset=utf-8";
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream myResponseStream = response.GetResponseStream();
            StreamReader myStreamReader = new StreamReader(myResponseStream, System.Text.Encoding.UTF8);
            string retString = myStreamReader.ReadToEnd();
            myStreamReader.Close();
            myResponseStream.Close();
            var obj = new
            {
                data = retString,
                Success = true
            };
            Formatting microsoftDataFormatSetting = default(Formatting);
            string result = JsonConvert.SerializeObject(obj, microsoftDataFormatSetting);
        
            HttpContext.Current.Response.Write(result);
        }