My timer stop for unknown reason

Hello,

I have an issue with my below timer that for some unknown reason stop working (specially the week-end).

I have created in my global.asax.cs file this timer.
I have setup the app pool that run the servive to IdleTime = 0 and set Always running in the SafeMode to make sure the service is always up and running.

 public class Global : System.Web.HttpApplication
        {
        private static readonly Timer _timer = new Timer(OnTimerElapsed); 

        private static void OnTimerElapsed(object sender)
            {
        
            CODAIntegration.Business.BusinessAccessLayer.CreateStatusXML() ;
            }
        protected void Application_Start(object sender, EventArgs e)
        {
            _timer.Change(TimeSpan.Zero, TimeSpan.FromMilliseconds(int.Parse(ConfigurationManager.AppSettings["StatusLastTimerMin"].ToString())*60000));            

        }

the CreateStatusXML() add an entry in the db so I can control when Timer is running.
for unknown reason the timer Stop working. (the service is less used during the Week-end)

It's like the Timer thread was stopping after some unactivity.

did I forget something ?