A couple of months back, out of the blue, my HTC Hero stopped notifying me on my upcoming calendar events. It didn’t even show upcoming events on the home screen widget, but it kept syncing new events without a problem.

I tried adding and re-adding the calendars I sync on the phone, turning on/off the notifications but nothing worked. I found a link to a guy who had the same problem, which ended up being caused by him force quitting the alarm service. But I had not done that, and either way it should’ve started working after a reboot if that were the case. Another guy managed to get his notifications working after doing a factory defaults reset.

Resetting to factory defaults isn’t my first choice of action, so I searched for, and found, a way to reset the calendar instead. And after doing that a test notification I set to go off a couple of minutes earlier got synced back to the phone and went off!

On your phone:

Settings -> Applications -> Manage applications
Open up Calendar storage and press Clear data.
I also cleared the Calendar app, not sure if it was needed though.

Posting in hope that if anyone else have this problem they won’t have to rummage through the internet as I did.