well, I'm not really into Python, but D3D suggests (*) that scripts may fail when their start-up runs while Poser is not fully initialized yet, and suggests a specific delay(...) routine to handle that.
My suggestion is that any value currently used (say 1000 msec) might be (just) too small on some machines, in some situations, for whatever reason, giving the fail a random character. Then increasing the delay (or making it variable, or ...) might be a way out.

(*) the PDF is protected, I can't quote from it.  Just check out his site: d3d.sesseler.de in the Poser Tutorials section.

Be aware: I do know my way into programming but not into Python. I'm just thinking out loud, backed by 37 years coding experience, some reading, and some fantasy. I've seen this kind of timing issues in some of my own projects as well. But the cause might be entirely different, though.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though