This might be the reason, give it a try ...
Sometimes ADE gets its registration/activation confused and in a semi-authorized state.
Uninstalling and reinstalling does not help.
Unfortunately, it often then gives misleading error messages about what is wrong.
A common incorrect message informs you that the ID is already in use on another computer and cannot be reused.
This can often be resolved by completely removing any authorization using ctrl-shift-D to the Library screen on ADE (cmd-shift-D if on Mac).
Restart ADE, and then reauthorize with your (old) Adobe ID.
OK, I have completed getting my computer authorized for DRM through Adobe Digital Editions-2. When I tried to open up one of the ebooks that I am having a problem with I received this note:
UNLOCK code needed
To open this item on your computer, enter the account user name and the unlock code associated with the item, then click on the open button.
I put in my user ID and my pass code and it was incorrect! Now what is the problem?
Regards, Ed Weber
I've never seen that message.
Some suppliers use a secondary authorization mechanism in conjuction with Adobe DRM.
I'm not quite sure how that works; but maybe your unlock code is to do with that.
I have heard that for some publishers, the credit card number used for the purchace is used as a key of some sort.
Probably best to check with the bookseller from whom you purchaced the book.