Imagine waking up and having your arm replaced by a cube! I think this is an incident (a corruption in the file), I have never had it happen in my long Ray Dream / Carrara history. But I did have my share of files that no longer could be openened, which happened after a save gone wrong (across a network for instance). I got myself accustomed to saving multiple versions (stages) of things I am working on, mostly because of files getting weird... Good luck!