There's only a single accoount on my PC and it's a standard installation. I'm the only person who ever uses it.
The first time it happened I hadn't used beaTunes for a month or so and it opened up in a small window with the 'trial license' message. However, the second time it happened I had been using it the day before. When I re-entered the license it had remembered my library and playlists but most other settings had returned to their defaults.
I did notice that Java updated the day before - could that have anything to do with it?