The only time that happened to me (so far) was when I managed to set a scene in the middle of an animation sequence (don't ask....I wasn't doing animation). When I clicked a few slides past the first one, my scene came back to me. Why it was in the middle of a sequence of 30, I don't know, but there it was. Poser has a mind of its own, doesn't it? Unfortunately, sometimes it seems deranged.