Until you get this fixed, then on your Desktop:
1.) DO NOT REGISTER ADE with your current AdobeID (this will mean that you will not be able to read the book anymore), until you get this fixed.
2.) DO NOT PURCHASE any more ebooks
Your best bet would be to ask wherever you purchased the book, for a redownload (with a new transaction ID), and to download it on your notebook. If you can do this then you can register your Desktop with your AdobeID and you'll be fine.
Outside of that you've got two choices:
1.) Register your desktop with a brand new AdobeID, and authorize your Bookeen with that so you can read your new book (but not your old books - and then switch as needed) - I would recommend this
2.) Re-purchase the book somewhere with better customer support (so that if you get into this situation in the future....)
3.) Read it on your desktop, and delete it when you are done (and then register ADE with your AdobeID, so that you don't accidently do this for any other books).