Some daily and weekly reminders have stopped, some haven't

I have a couple of different reminders, 4 marked @weekly and one marked @daily, that have stopped sending email reminders to me. the marked @daily faithfully sent me a reminder every day for four days, then stopped. the reminder still shows up on my calendar, but i don't get the email. same deal with a my weekly reminders, except they went for 6 weeks consistently, then stopped sending reminders. i am not aware of any time that i asked sandy to edit the settings on the calendar items. i had three @weekly reminders set to show up on monday morning, and this week i only got one of them. what am i missing?