My application shows a balloon in tray when it's done processing a task. This works ok - but if the application is not in focus when the balloon is supposed to be shown, i get this error: "Object reference not set to an instance of an object."

Here's the code:

        public void show_balloon(String title, String text)
        {
            tray.ShowBalloonTip(50, title, text, ToolTipIcon.Info);
        }

Does anyone know what causes this?