FormsAuthenticationTicket tkt;
string cookiestr;
HttpCookie ck;
tkt = new FormsAuthenticationTicket(1, _user.User_Id.ToString(), DateTime.Now,
DateTime.Now.AddMinutes(60), true, string.Format("{0},{1}",     System.DateTime.Now.ToString(), _user.User_Id.ToString()));
cookiestr = FormsAuthentication.Encrypt(tkt);
ck = new HttpCookie(FormsAuthentication.FormsCookieName, cookiestr);
ck.Path = FormsAuthentication.FormsCookiePath;
Response.Cookies.Add(ck);