I have Adobe Digital Editions 2.0 I am trying to authorize it , but for the past months I have been getting this as an error message:
Activation server error
I have tried setting up new Adobe IDs and have even tried uninstalling and then reinstalling Adobe Digital Editions.
Try explicitly deregistering ADE. It sometimes gets itseft in odd half-registered situations; which even uninstalling and reinstalling will not remove.
Run ADE, hit ctrl-shift-D (cmd-shift-D on Mac), restart ADE (maybe not necessary), and try again to register.