BasePage.cs

    public class BasePage : System.Web.UI.Page
    {
        public BasePage()
        {

        }
        protected override void OnInit(EventArgs O)
        {
            if (base.Session["username"] == null || base.Session["username"].ToString().Equals(""))
            {
                Response.Redirect("~/index.aspx");
            }
            base.OnInit(O);
        }
    }