ClaraG: do you know how to use the Terminal on Mac OS X?
You should try this:
Open Terminal.app
type
Code:
cd "/Volumes/Cybook\ Opus"
then
Code:
rm -Rf .adobe-digital-editions
Now, quit Terminal, eject and unplug your Opus, and reboot it. Then the next time you will plug you Opus with ADE started, it will ask you for authorize the device. If this does not work I don't know what can happen...