หามาหลายวันแล้วค่ะ ยังไม่เจอเลย error ExecuteReader: Connection property has not been initialized.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Drawing.Drawing2D;
using System.Diagnostics;
using BookRent.Class;

namespace BookRent
{
    public partial class frmReturn : Form
    {
        public frmReturn()
        {
            InitializeComponent();

            
        }

        SqlConnection Conn;
        //SqlCommand com;
        //StringBuilder sb;

        SqlDataReader dr;
        DataTable dtMember;
        SqlTransaction tr;

        DateTime Today;
        
        string CRentID = "";
        string[] CurrentBook = new string[10];
        
        Stopwatch sw = new Stopwatch();
        //double ProcessTime;
        //ToolStripLabel _ToolStripLabel = new ToolStripLabel();

        private void frmReturn_Load(object sender, EventArgs e)
        {
            this.WindowState = FormWindowState.Maximized;
            //lblBranch.BackColor = Color.FromArgb(0, 0, 0, 0);
            lblFine.BackColor = Color.FromArgb(0, 0, 0, 0);
            grbDetail.BackColor = Color.FromArgb(0, 0, 0, 0);
            grbProductList.BackColor = Color.FromArgb(0, 0, 0, 0);

            sw.Reset();
            sw.Start();

            string strConn;
            strConn = DBConnString.strConn;
            Conn = new SqlConnection();
            if (Conn.State == ConnectionState.Open)
            {
                Conn.Close();
            }
            Conn.ConnectionString = strConn;
            Conn.Open();

            Today = DateTime.Today;

           

            

            ClearAllData();
            txtSearchMember.Focus();

            sw.Stop();
            
        }

        private void ClearAllData()
        {
            lblNetFine.Text = "0";
            txtSearchMember.Text = "";
            lblFullName.Text = "";
           // lblFineRateDiscount.Text = "0";

            dgvMemberList.Visible = false;
            dgvRent.DataSource = null;
            dgvRentDetail.DataSource = null;
            dgvBookList.Rows.Clear();

            CRentID = "";
            cmdCalculateNetFine.Enabled = false;
            cmdExchange.Enabled = false;
            cmdSave.Enabled = false;
        }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace BookRent.Class
{
   public sealed  class DBConnString
    {
       public static string strConn = "Data Source=.\\SQLExpress;Initial Catalog=dbBookRent;Integrated Security=True";
        
        public static string UserName = "";
    }
}