ASP.Net Identity 2.0 Can't Login after One user Logined

I use visual Studio 2013, ASP.Net Identity 2.0, Web Forms Application , I create simple Project Where Session["MySessionVariable"] value set in button click

, after session is set I cannot to login in Page from other browser, same or other user , why whats wrong.
After ISS restart and before session set user login worked fine

Here is my code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1
{
    public partial class _Default : Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            Session["MySessionVariable"] = "aq145";
        }
    }
}
Thanks in advance