What steps are you taking exactly?
I would usually expect to do the re-activation first, not associated with any book, using menu/Help/Authorize Computer (menu/Library/Authorize Computer on v1.72)
And then to access the book once the reactivation had happened.
In that case, the reactivation would not be associated with any book and the message you quote would not make sense.
Unfortunately, many ADE messages are incomprehensible,
and there are quite a few circumstances where the messages are quite comprehensible but don't actually say what they mean.
One possible solution .... I'm not at all sure if will help, but it has helped a lot of people in very varied situations.
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
Thanks for your help. I’ll be away from my computer for a couple of days but will try installing v 1.72 of ADE when I return.
One further question now -
is the vendor name supposed to be ‘Adobe ID’ while doing this authorization to use for obtaining books from my public library?
Yes, overdrive books use a generic Adobe ID for authorization.
Some vendors use the Adobe DRM system, but with their own vendor specific user/password combinations.