activation server error

Please try the below steps (read the note section before clearing the registry):

Mac:

1. Deauthorize ADE. To do so, navigate to /Users//Library/Application Support/Adobe/Digital Editions and drag the activation.dat file to trash.
2. Authorize ADE again.

Windows:

1. Click Start > Run.
2. Type regedit and then press Enter. The Registry Editor opens.
3. In the left pane of the Registry Editor, locate the following registry key: HKEY_CURRENT_USER\Software\Adobe\Adept
4. Right-click the Adept key and click Delete.
5. In the Confirm Key Delete dialog box, click OK. ADE is deauthorized now.
6. Authorize ADE again.

Note:

Deleting the registry will deactivate all ADE authorization credentials on this computer. You will then be able to open eBooks on this computer only if you know your authorization credentials. Also you will not be able to open books that are fulfilled using anonymous accounts (authorized computers without an ID).