The ShowBalloonTip method allows you to provide a System.Drawing.Icon object to show a custom icon in the balloon notification. However, the method doesn't work when this overload is used. The balloon notification is not displayed at all. 

To work this around, use the predefined BalloonTipIcon icons with the additional overload of the method.

notifyIcon.ShowBalloonTip( "title", "text", BalloonTipIcon.Warning);