สอบถามปัญหาเรื่องดึงข้อมูลจาก mysql และการสร้าง chart Series data point dot not support value of type System.TimeSpan

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using MySql.Data.MySqlClient;
using System.Web.UI.DataVisualization.Charting;


namespace RAIN
{
    public partial class _Default : System.Web.UI.Page
    {
        MySql.Data.MySqlClient.MySqlConnection objConn;
        MySql.Data.MySqlClient.MySqlCommand objCmd;
        protected void Page_Load(object sender, EventArgs e)
        {
            this.Title = "ANALYSIS RAIN";
            String strConnString;
            strConnString = "Server=localhost;User Id=root; Password=123456; Database=mysql; Pooling=false";
            objConn = new MySql.Data.MySqlClient.MySqlConnection(strConnString);
            objConn.Open();
        }
        void BindData()
        {
            String strSQL;
            strSQL = "select*from rain WHERE (DATE) = ('"+D+"');";
            MySql.Data.MySqlClient.MySqlDataReader dtReader;
            objCmd = new MySql.Data.MySqlClient.MySqlCommand(strSQL, objConn);
            dtReader = objCmd.ExecuteReader();

            //*** BindData to Repeater ***//

            Repeater1.DataSource = dtReader;
            Repeater1.DataBind();

            dtReader.Close();
        }
        public string D
        {
            get { return Calendar1.SelectedDate.ToString("yyyy-MM-dd"); }
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            BindData();
            Label1.Text = D;
        }
    }
}