Dson is a Poser 'addon', a special kind of script that is automatically loaded if it is present in any linked runtime. Reality is another. Addons are found in this folder (of any runtime): Runtime Python addons

If it is a compiled file (*.pyc), then it needs to have been compiled with the same version of Python under which you are now trying to run it.

If you don't want an addon to run when you load Poser, then remove its folder from the 'addons' folder of the linked runtime. If you want, you can put all the addons in a separate runtime which contains nothing but the addons. That way you can link Poser 11 to that runtime, but not Poser 12.

Free stuff @ https://poser.cobrablade.net/