ajax rating control onchange fires twice

hello 

ive posted this problem before but didnt get response

ive a rating control whose onchange event fires twice when i click on the stars ive no idea why here is the code

markup

<ajaxToolkit:Rating ID="Rating1" runat="server"  StarCssClass="Star" WaitingStarCssClass="WaitingStar" EmptyStarCssClass="Star"
    FilledStarCssClass="FilledStar" CurrentRating="1" OnChanged="Rating1_Changed"></ajaxToolkit:Rating>

code behind file

protected void Rating1_Changed(object sender, AjaxControlToolkit.RatingEventArgs e)
        {
            int VV = 3;

            string constr = ConfigurationManager.ConnectionStrings[1].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                using (SqlCommand cmd = new SqlCommand("INSERT INTO Rating VALUES (@rating,@id)"))
                {
                    using (SqlDataAdapter sda = new SqlDataAdapter())
                    {
                        cmd.CommandType = CommandType.Text;
                        cmd.Parameters.AddWithValue("@rating", VV);
                        cmd.Parameters.AddWithValue("@id", '1');
                        cmd.Connection = con;
                        con.Open();
                        cmd.ExecuteNonQuery();
                        con.Close();
                    }
                }
            }

           
            

        }

any ideas?