All I can suggest is a little more exploration that won't directly lead to a result, but may help towards one.
Are you running ADE2.0/2..0.1 or the older v1.7.2?
v1.7.2 is generally more reliable, but 2.0 will give a bit more information that can be helpful if you are willing to dig.
On 2.0/2.0.1, type ctrl+shift+I (Help/Authorization Information) and it will give details about your registration,
including the internal Adobe ID (urn:uuid)
You can check the registration (internal Adobe ID) the book is authorized with by this irritating route ...
open a sample DRM .epub file as a .zip file.
With some zip programs, you can just open the .epub as an archive (ev, with 7zip),
with others you will have to rename the .epub file to a .zip file first, then open it.
find the file 'rights.xml' within the zip. Probably 'META-INF\rights.xml'
open the rights.xml file
inside you will find a section '<user>' that looks something like
<user>urn:uuid:ff2ddc22-eca0-46c6-a84d-xxxxxxxxxxxx</user>
If those urn's match, you should be able to read the book.
If they don't, the book is registered to the wrong user.
Unfortunately, I don't know of a way to find the useris (email) currently associated with the given urn:uuid