Error 1503 on lunching windows service

Try this and put the IvrApplication.Start in the OnTimed Event

//In OnStart
System.Timers.Timer aTimer = new System.Timers.Timer(500); //500 MilliSeconds
            // Hook up the Elapsed event for the timer.
            aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
            // Set the Interval to 2 seconds (2000 milliseconds).
            //aTimer.Interval = 600000;  //10 minutes //2000; //2 seconds (2000 mili seconds)
            aTimer.AutoReset = false;
            aTimer.Enabled = true;
            //Console.WriteLine("Press the Enter key to exit the program.");
            //Console.ReadLine();
            // Keep the timer alive until the end of Main.  This allows OnStart to close in a timely manor.
            GC.KeepAlive(aTimer);
        }
        // Specify what you want to happen when the Elapsed event is 
        // raised.
        private static void OnTimedEvent(object source, ElapsedEventArgs e)
        {
             IvrApplication.Start();
        }

One question... Are you sure that code you are running is not an Application users interact with?