Ah. A used copy would indeed be useless due to the authentication method unless the prior owner planned on transferring their account to you (unlikely since it's partly tied to one's credit card information for online purchasing). I haven't used the retail version, but I'm pretty sure that it works pretty smoothly. You activate it, choose your free gaming system, and set up your account all at the same time. Posting to The Hero Lab section
of the Lone Wolf forums might get you an answer from someone with more experience. The one mention I found was that some of the retail copies are older ones when only d20 OGL was supported
which necessitates downloading the recommended update prior to selecting your game system.
^_^ Best of luck!