using WebMessageBodyStyle Wrapped

I am getting 400 bad request for WebMessageBodyStyle.Wrapped

<b><u></u>Interface</b>

public interface ITMCOtherService
    {
        /// <summary>
        /// Searching nearest post office and ATM machine loations
        /// </summary>
        /// <param name="SearchbyLatLonRequestData"></param>
        /// <returns>returns response nearest post office and ATM machine address</returns>
        [WebInvoke(Method ="POST",
            ResponseFormat=WebMessageFormat.Json,
            RequestFormat=WebMessageFormat.Json,
            BodyStyle=WebMessageBodyStyle.Wrapped,
            UriTemplate = "api/10/map/search/latlng/")]
        [OperationContract]
        string SearchbyLatLon(string SearchbyLatLonRequestData);


<b><u></u>Serialization</b>

 public static string ConvertToJSON(this object obj)
        {
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            return serializer.Serialize(obj);

        }

<b>Console App</b>

 public void BranchLocatorUsingLatLong()
        {
            SearchbylatlongRequest.RequestRootObject rootObj = new SearchbylatlongRequest.RequestRootObject();
            var data = new SearchbylatlongRequest.Data
            {
                ApiKey = "0de82ab2-5741-433b-a48b-97302383c608",
                UDID = "45612312312312321",
                AppUserAgent = "AppuserAgent = Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_3_3 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8J2 Safari/6533.18.5",
                AppVersion = 1.2,
            };

            var Params = new SearchbylatlongRequest.Params
            {
                Lat = 51.439425,
                Long = 0.417455,
                FilterType = 3,

            };
            rootObj.data = data;
            rootObj.Params = Params;
            string ServiceUrl = System.Configuration.ConfigurationManager.AppSettings["FRESOtherService"] + "/map/search/latlng/";

            WebClient WC = new WebClient();
            WC.Headers["Content-type"] = "application/json";
            MemoryStream MS = new MemoryStream();
            DataContractJsonSerializer JSrz = new DataContractJsonSerializer(typeof(string));
            string json1 = Helper.ConvertToJSON(rootObj);
            JSrz.WriteObject(MS, json1);
            System.Text.UTF8Encoding en = new System.Text.UTF8Encoding();

            byte[] res1 = WC.UploadData(ServiceUrl, "POST", MS.ToArray());
            MS = new MemoryStream(res1);
            JSrz = new DataContractJsonSerializer(typeof(string));
            string result = (string)JSrz.ReadObject(MS);
            Console.WriteLine(result);
            Console.ReadLine();

        }