It was a quiet December evening. In the distance, a chime rang. Suddenly, an Outlook Reminders window appeared on my desktop.
This is an actual picture of the window as it appeared at the time. The window would not resize. The window would not maximize. I made torturing gestures with my mouse, but the window held my reminders as closely guarded secrets.
I poked around with the registry editor and found a value named WindowPos under HKCU\Software\Microsoft\Office\11.0\Outlook\Options\Reminders. Deleting this value and restarting Outlook made the Reminders window appear with a normal, visible size. Problem solved ...
... except, I couldn't remember what I was working on before my reminders appeared.