Try one of the following solutions:
Solution 1: Reset the eBook Reader client.
If you don't have any eBooks that you want to retain, reset the eBook Reader client by deleting the contents of the following folders:
-- My Document/My eBooks
-- Documents and Settings/[user name]/Application Data/Adobe/Acrobat/6.0/eBooks
-- [User name]/Library/Acrobat User Data/eBooks
Solution 2: Reactivate eBook Reader using your original ID.
If you have eBooks that you want to retain, reactivate eBook Reader using the same Microsoft .NET Passport ID or Adobe ID that you originally used to activate eBook Reader.
To activate eBook Reader using your original ID:
1. Go to the Adobe DRM Activator Site on the Adobe website at http://aractivate.adobe.com.
2. Log in with the same .NET Passport ID or Adobe ID that you originally used to activate eBook Reader.
3. Click Activate and wait for the activation process to complete. When activation is complete, you'll be able to open your eBooks.
This error occurs if you originally activated eBook Reader using a .NET Passport ID or an Adobe ID, and then try to reactivate eBook Reader using a different ID.