If you find out how to fix this, or how to prevent it from happening, please let me know. I lost several hours and quite a bit of hair to exactly the same problem on Friday, with the added bonus that I was working on a paid project. No amount of tinkering solved the issue: restarting poser, restarting the machine, or even opening "previous" versions of the file; I had two main characters in it and alternatively one or the other would lock eventually. In the end, I had to start again the whole thing from scratch in P5, and save just before adding lighting to open and render in P6. But I wasn't a happy bunny.

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