Close all applications.
Press WINDOWS + R.
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
Remove the Adept Folder.
In the Confirm Key Delete dialog, click OK.
Close the Registry Editor.
Open Adobe Digital Editions and reauthorize..
quit Adobe Digital Editions.
Navigate to /Users//Library/Application Support/Adobe/Digital Editions and drag the activation.dat file to the trash.
If you are using 10.7, see https://helpx.adobe.com/x-productkb/global/access-hidden-user-library-files.html
Open Adobe Digital Editions and reauthorize.
Thank you so much Nanaky. You finally found the solution to my problem. I'm really happy!