Quote - So the reason I didn't have this problem before with Poser 5-9, is because of what?

Luck.

Poser 8 I believe introduced wxPython 2.8, in Poser 9 it was updated to wxPython 2.9 which I think lives in separate files and folders. Copying files from Poser 8 to Poser 9 would then not overwrite files but only add files that Poser 9 would ignore. Poser 10 still uses wxPython 2.9, but includes minor updates and bug fixes that make the dlls from one version incompatible with the other (all scripts should still work as before).