I have a calender reminder box that pops up with 3 reminders (which are overdue by several years) and these reminders will not go away. It will not let me snooze all or dismiss all or in anyway modify the screen. It just sites there until I close eM, and then they pop up again every time I open it. I have just installed your desktop client and really like it. I may upgrade to pro. I do wish it had some good printing for daily calendars! That is one major flaw!
You could go to the Calendar and clear the reminder from each of those three events manually.