protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {

        Session["CourseDate"] = lblCourseDate.Text.ToString().Trim();

        Response.Redirect("~/Invoice/PrintInvoice.aspx");

    }

protected void Page_Load(object sender, EventArgs e)
    {

        lblCourseDate.Text= (string)(Session["CourseDate"]);

    }