c# jsonpost 数组　不成功

本人要post json 数据，数据里出现数组memberList时post返回"Unknown property 'memberList'"错误 ，去掉memberList数组post成功，不明白？？

     string temp2 = "{\"memberList\":[{\"userId\":\"\",\"userName\":\"吴\",\"userPhone\":\"1382562699\"}],\"distCode\":\"44120100003\",\"beginTime\":\"2015-10-10 08:00:00\",\"script\":\"12语音\",\"endTime\":\"2015-10-10 18:00:00\",\"activityName\":\"任务名称\"}";

               string strUrl = @"http://10.150.29.234:9080/ocmx2/activity/taskDetail.action";
               HttpWebRequest request = (HttpWebRequest)WebRequest.Create(strUrl);

               request.Method = "POST";

               request.ContentType = "application/json;charset=GBK";

               byte[] payload=System.Text.Encoding.GetEncoding("GBK").GetBytes(temp2);

               //将Json字符串转化为字节
               //设置请求的ContentLength
               request.ContentLength =payload.Length;
               //发送请求，获得请求流
               System.IO.Stream writer;
               try
              {
                 writer = request.GetRequestStream();//获取用于写入请求数据的Stream对象
              }
                 catch (Exception)
              {
                 writer = null;

               }
                //将请求参数写入流
                writer.Write(payload, 0, payload.Length);
                writer.Close();//关闭请求流
              //  String strValue = "";//strValue为http响应所返回的字符流
                HttpWebResponse response=null;
                try
                {
                //获得响应流
                response = (HttpWebResponse)request.GetResponse();
                }
                catch (WebException ex)
                {
                   //  response = ex.Response;
                }
                string StrDate = "";
                string strValue = "";
                   System.IO.Stream s =response.GetResponseStream();
                   System.IO.StreamReader Reader = new System.IO.StreamReader(s, Encoding.GetEncoding("GBK"));
                   while ((StrDate = Reader.ReadLine()) != null)
                   {
                       strValue += StrDate + "\r\n";
                   }
                   textBox2.Text = strValue;

                s.Close();