ical events disappear (only future ones) after time machine backup

I did a time machine back up and then I was getting notices from folks asking why I "cancelled" my meetings with them. What's odd is that all of iCal event IN THE FUTURE were gone, but not the ones in the past. So it's not like the events were just deleted. No, my network actually got "This event is cancelled" notifications?

WTH?

Any ideas on how to fix this?