Does it matter where the default calendar is located? I thought the one under "My Calendars" was the default associated with my email address and needed to be kept. That is the one it appears I could delete. I think I'll do a complete backup before trying this. :-)

The one I cannot delete is under "Other Calendars", along with a shared calendar I subscribe to. I put this one, named Calendar, into list view and there were only 6 items which I promptly deleted; that calendar, the original, is now empty. To my surprise, none of the 6 items deleted were recurring items. They couldn't have been responsible for the annoying duplicate reminders. It appears duplicate reminders occur simply because there are two instances of Calendar. Non-recurring items do not produce extra reminders. Even more peculiar is that when my subscribed calendar was accidentally is duplicated, I got even more reminders, even though these calendars have an entirely different name and contain NO recurring items. The number of duplicate reminders can be predicted but this behavior would appear to be a bug.