I think there is a problem with iCal's alarms whereby, under certain circumstances, they do not go off. I missed a couple of events that I had set up iCal reminders for and at first I thought I had just made a mistake, but on further investigation I'm able to duplicate this problem. I'm wondering if anyone else is able to duplicate this on their Macs:
1. Set an appointment for an event at least 24 hours from now and set the alarm for 18 hours before the event occurs.
2. When the 18-hour alarm comes up, set it to remind you again two hours before the event.
The problem is that the second alarm never occurs.
Other details of my computer:
iMac G5
OS X Tiger 10.4.1
iCal 2.0.1
I leave iCal running all the time with the calendar window closed most of the time (so that the icon in the dock has the correct date).
My computer is always on and set never to sleep.