WCF with JSON Undefined Error

function CallMyService() {
          $.ajax({
              type: "POST",
              url: "http://localhost:82/BookingRequest.svc/AutoSuggestBookPanel?prefixText=Australia&ReturnType=json",
              contentType: "application/json;charset-uf8", // content type sent to server
              dataType: "json", //Expected data format from server
              success: function (msg) {
                  alert(msg);
              },
              error: function (response, textStatus, errorThrown) {

                  alert(response.responseText);
                  alert(textStatus.responseText);
                  alert(errorThrown);
              }
          });
      }

[OperationContract]
      [WebInvoke(Method = "POST", BodyStyle = WebMessageBodyStyle.Wrapped, RequestFormat = WebMessageFormat.Json, ResponseFormat = WebMessageFormat.Json,
          UriTemplate = "/AutoSuggestBookPanel?prefixText={prefixText}&ReturnType={ReturnType}")]
      String AutoSuggestBookPanel(String prefixText, String ReturnType);