blast but i can't find the email from adobe support that fixed this problem. [assuming that you have set this kind of file to open with digital editions: i only know how to do that on a mac. highlight the file and get info. then change. i think for windows you highlight then get a menu opening choose properties? and set to open with digital editions.]
for the mac version: i had gotten two responses.
one was to rename the restore folder within the digital editions folder within documents to restore.bad.
the second was to delete some macromedia preference. this is the one i think has to be done but can't find which pref gets deleted.
Aswell as the last suggestion, it's worth checking the two things below also.
1) Ensure you are running the latest version of ADE. If you rejected the option to upgrade (a new release was made available in May) then a bug in the previous version of Digital Editions meant that no new books could then be viewed and you would see a blank screen. Ensure you accept any upgrade requests.
2) Check your computer firewall/antivirus software isn't blocking access to the Adobe Activation server. When Digital Editions opens a file, it needs to talk to the Adobe activation server to validate the document is genuine. If you can visit http://adeactivate.adobe.com (the activation server) and you see a welcome screen, then you can see the server. Although this doesn't mean that Digital Editions can see it, you may need to play around with your firewall settings to ensure that Digital Editions itself is allowed to communicate with the activation server.