It got me scratching my head for a while on why my session state was being reset every time I go to a different page. After careful look, what I realized is I was doing a Response.Redirect on a control's event which was inside atlas:update panel. I looks like atlas redirects the page but with new session state everytime you try to redirect from an event which is an atlas control. My solution, simply remove that control from the update panel and place it on the page or use different redirect mechanism instead of redirecting after the event fires.