I got the same error trying to see how many trees I could put in a scene. I had twenty or so on the screen. Halfway through the render, the same message popped up. Alas, I had not saved. I haven't tried to repeat the error. Pesky life gets in the way and keeps me from spending as much time on the computer as I want. Bryce always has been a little uptight once the scene gets above a hundred Meg or so. The limit is always a little different foir each scene, but I usually think about saving often when the machine starts grinding on the hard drive.