I have a Macintosh running Mavericks, 10.9.5 and was running Adobe Digital Editions 2 happily and then made the major error of trying to "update" to Adobe Digital Editions 4.0.2 -- and the installer crashed. Now when I try to run Adobe Digital Editions 4.0.2 it just crashes, and restoring Adobe Digital Editions 2 from Time Machine gives me an app that does not open.
Any advice other than never trying to use Adobe Digital Editions again, and remembering Adobe as a company that does not support it's products?