After recently upgrading Thunderbird to 17.0.2 I created a new event. When the event notification appeared, I was not able to dismiss or delete it. It continually pops-up as a reminder and I can not edit it or delete it within Thunderbird. After several days of annoying reminders, I did delete it from Beehive, but it is still in Thunderbird and popping up every 30 minutes or so. How can I permanently delete this event?