What happens when you try to erase and deregister it? What error are you given?
You may also want to take it back to Walmart and show them. It seems unlikely that you got a demo unit and more likely that you got a return that was repackaged.
Also, please not that this is the wrong forum, the Tablet forums are for Nook Tablets. You should post in the Nook Simple Touch or eInk devices forums. Don't worry about re-making this post there, just something to be aware of for the future. Posting in the correct forum will make it easier for people to help you.