Add an Action Filter in MVC to solve problem of Authentication Timeout. Once Authentication Timeout then redirect to another place.
public class AuthenticationTimeoutFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting( ActionExecutingContext filterContext ) {
HttpContext context = HttpContext.Current;
if (!context.User.Identity.IsAuthenticated)
{
context.Response.Redirect("~/ControllerName/ActionName");
}
base.OnActionExecuting ( filterContext );
}
}

Forms Authentication timeout default in ASP.NET 2.0