public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                if (Session["IsExecExport"] != null)
                {
                    TextBox1.Text = Session["IsExecExport"].ToString();
                }
            }
        }

        protected void Button2_Click(object sender, EventArgs e)
        {
            Response.Redirect("Default.aspx");
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
           System.Threading.Thread t = new System.Threading.Thread(new System.Threading.ThreadStart(Add));
            //t.IsBackground = true;
            t.Start();
        }

        private void Add()
        {
            Session["IsExecExport"] = "1";
        }
    }