Try this - Logout button event:

String pageUrl = "";
pageUrl = Request.Url.ToString();
Session.Abandon();
Response.Redirect(pageUrl);

- And in other page that need session to work try

protected void Page_Init(object sender, EventArgs e)
{
Response.Cache.SetNoServerCaching();
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Cache.SetNoStore();
Response.Cache.SetExpires(new DateTime(1900, 01, 01, 00, 00, 00, 00));
}