Oh I remember that thing about not being able to delete Simon. I can't remember now how I got around it, but you might try holding down the Shift key while pressing the Del key.
That prevents Poser from trying to store it into memory as an undo, which could be the problem.
It'll tell you that this action is not un-doable, but I think it should work. Then just try saving out a new startup preferences by going to Edit>General Preferences and setting the startup state to No Simon.
Or you could just save out a blank empty .pz3 scene.

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