I have this exact same problem and it has nothing to do with moving folders etc.
I finally created a DVD project I was happy with after having worked on it for days, the purpose of which was to create a template to do future DVDs from…… and now I’ve lost the work….
Luckily I have some project backups I made but that still means I’ve lost a day’s progress.
It isn’t even as though Encore automatically backs up files every n minutes…..
This is my first professional experience with Encore and if this is a sign of things to come, I can’t work like this.