Seems a problem with the permissions. You user has no permissions to save the authoriation under your System and must ask again and again.
How do I give myself permission to save the authorisation? What is it saving, and where, when it saves the authorisation?
How you give the right permissions should contact the support of your OS. /Users//Library/Application Support/Adobe/Digital Editions
You need full permissons to this folder: /Users//Library/Application Support/Adobe/Digital Editions
Got it :-)
There wasn't a 'Digital Editions' folder in the library, but once I'd given myself permission to read/write '/Users//Library/Application Support/Adobe' and authorised the ADE, it then created the folder.