You must make sure your copy of ADE is registered with an explicit Adobe ID, and that the Kobo is also registered with the same ID.
If you haven't done so already,
There are lots of bugs in ADE2.0.
One is that it refuses to work at all with some devices,
another that it refuses to work for library books with some devices (including many Sony eReaders).
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
I have the same problem - in May 2015! Have downloaded ADE 4.0