Onetime event with date and alarm set in the past is called an expired event. For instance, if you make Onetime event to
remember the business meeting at January 21st 2000 at 13:00h, that event becomes expired when that date and time passes. Expired events are detected first time you
left click with your mouse on Reminder's tray icon to show Calendar, or when you choose Check expired in
File form. For first case, in Config you can setup Reminder to:
1) Ask what to do (delete or ignore)
2) Automatically delete expired events
3) Ignore expired events