When you open a book in Adobe Digital Editions, you get an error stating that another user account has the book locked:
This error indicates that the book is already downloaded using another account. Check that you are using the same account you used earlier to download the book.
If the account is the same, ask your e-book provider to issue a new ACSM token.
To check the Adobe ID currently used to authorize Adobe Digital Editions, choose Library > Authorize Computer.
This error occurs because the book is assigned to another user, or you have tried to deactivate an anonymous activation and create a named activation.
Once deactivated from an anonymous login, that there is not going back to that same anonymous login.