I would assume that since it has already validated your ownership of the script once, that it is just checking that you are entering the same credentials as you did when you were online.

Why is it necessary to even enter those credentials? Because presumably if you did not have to do so, you could copy those files to another computer and bypass the activation. In this case, even if you could, you wouldn't give those files to someone else knowing they would need to get your credentials.

It's not a perfect solution for anyone -- personally I'd rather Poser not call home at all -- but I understand where they are coming from.