If due to some reason, you are unable to deauthorize ADE, follow the below steps:
Mac: Navigate to /Users//Library/Application Support/Adobe/Digital Editions and drag the activation.dat file to the trash.
ADE will be deauthorized now.
Now Authorize ADE again.
Windows:
Choose Start > Run.
In the Open text box, type regedit and then press Enter. The Registry Editor opens.
In the left pane of the Registry Editor, locate the following registry key:
HKEY_CURRENT_USER\Software\Adobe\Adept
Right-click the Adept key and choose Delete.
In the Confirm Key Delete dialog, click OK.
Your authorization will be deleted.
ADE will be deauthorized now.
Now Authorize ADE again.