I have a new PC. I have transfered over my old email address (as you do). I want to authorise Adobe Digital Edition so I can load ebooks onto my eReader. Adobe will not let me Authorise my new PC as: "You can only authorise this computer with an Adobe ID that hasn't been previously used to authorise any other computer of mobile device." To me this appears to be a fatal floor - people update there machines and, at the same time, retain email addresses.
That is very likely an example of ADE getting its registration screwed up.
It is very happy to do this, and then often gives incomprehensible or incorrect error messages as a result.
Try completely removing authorization: ctrl-shift-D to ADE (cmd-shift-D on Mac)
Try again to authorize with your ID.