added a book without registering with an id, now cant download ebook

Hi, so I installed adobe digital editions and authorised without an id. I downloaded my ebook and found that I couldn't transfer to my ereader and had to create an adobe id. So i did that but now I cant open the book and get "The vendor account you entered is not associated with the item you are trying to open" instead.

How can I reset this or go back to using the old anonomous id?

thanks