Why webmethod is not called inside updatepanel in C#

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script type="text/javascript" src="http://cdn.jsdelivr.net/json2/0.1/json2.js"></script>

<script type="text/javascript">
        $(function () {
            $("[id*=btnSave]").bind("click", function () {
                
                var event1 = {};
                event1.EventDate = $("[id*=txtEventDt]").val();
                event1.Description = $("[id*=txtEventDesc]").val();
                $.ajax({
                    type: "POST",
                    url: "Default3.aspx/SaveEvent",
                    data: '{event1: ' + JSON.stringify(event1) + '}',
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    success: function (response) {
                        $find("mpe").hide();
                        clear();
                        __doPostBack('hdText', 'JavaScript');
                    }
                });
                return false;
            });
        });
        //==== Method to clear input fields
        function clear() {
            $("#txtEventDt").val("");
            $("#txtEventDesc").val("");                      
        }
    </script>

[WebMethod]
   [ScriptMethod]
   public static void SaveEvent(Event event1)
   {
       try
       {
           string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
           using (SqlConnection con = new SqlConnection(constr))
           {
               using (SqlCommand cmd = new SqlCommand("INSERT INTO Event VALUES(@EventDate, @Description)"))
               {
                   cmd.CommandType = CommandType.Text;
                   Default3 obj = new Default3();
                   string eventdate=obj.changeYYYYMMDD(event1.EventDate.ToString());
                   cmd.Parameters.AddWithValue("@EventDate", eventdate);
                   cmd.Parameters.AddWithValue("@Description", event1.Description);
                   cmd.Connection = con;
                   con.Open();
                   cmd.ExecuteNonQuery();
                   con.Close();

               }
           }
       }
       catch (Exception ex)
       {
       }
   }

protected override void Render(System.Web.UI.HtmlTextWriter writer)
    {

        ClientScript.RegisterForEventValidation("hdText", "JavaScript");

        base.Render(writer);

    }
    protected void hdText_Click(object sender, EventArgs e)
    {
    }