Below is a copy/paste from adobeforums.com posted by JimLester (i assume he works for Adobe). He seems to indicate in a few other posts that using the stand-alone installer produces better results.
Perform a clean uninstall:
1.)Uninstall current version 1.7
a) Windows - do the uninstall from the Control Panel
b) Mac - Delete \Application\Adobe Digital Editions.app
2.) Delete all the contents of the weird install location that begin with digitaleditions
WinXP
c:\Document and Setings\<user>\Application Data\Macromedia\Flash Player\
www.macromedia.com\bin
Vista
c:\Users\<user>\AppData\Roaming\Macromedia\Flash Player\
www.macromedia.com\bin
Mac
~/Library/Preferences/Macromedia/FlashPlayer/www.macromedia.com/bin
2.) Download Standalone Installer from:
http://www.adobe.com/cfusion/entitle...igitaleditions
3.) Launch Stand Alone Installer
This should end up with ADE launched and running
Make sure to remove any shortcuts/links you were using to find the old versions.