I'm not sure. Have you tried contacting Google?
No, and I'm not sure how and where would make most sense anyway.
I'd start here: http://www.google.com/support/calendar/?hl=en
Or specifically this one:
If you've noticed that you're no longer receiving event notifications, reset the calendar's notification settings to resolve this issue. To do so, follow these steps:
1. In the calendar list on the left, click the down-arrow button next to the appropriate calendar, then select Notifications. (Alternatively, click the Settings link at the bottom of the calendar list, then click the Notifications link to the right of the appropriate calendar.)
2. Click the remove link next to each reminder set in the Event reminder section.
3. Deselect any selected boxes in the Choose how you would like to be notified section.
4. Click Save.
5. Return to the Notifications settings page.
6. Enable your desired notification options again.
7. Click Save.
Thanks! I found the same information on their site by myself (because I only read the email notifying me of your reply before you edited the post - and not the post in the forum, hehe) and immediately tried it, but it's not working for me.
I now contacted Google's support, curious to see how quick (and how good) they are!