I have the same problem, who can help????? I use Windows Vista, after re installing Vista this problem occured...
Unfortunately, ADE2.0 is full of bugs.
You may be able to get round this one by uninstalling ADE2.0, and then reinstalling it.
(Check the Vista installation information at http://helpx.adobe.com/digital-editions/kb/installing-digital-editions-20-windows.html)
Failing that, try installing instead the older but more reliable ADE1.7.2.
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
In either case, it is quite likely that ADE will get its registration confused and half there.
In that case
- remove any corrupted registration by ctrl-shift-D (cmd-shift-D on Mac)
- restart ADE
- redo your registration (menu/Help/Authorize Computer on ADE2.0, menu/Library/Authorize Computer on ADE1.7.2)
I tried reinstalling etc and then got some technical assistance with my e-reader and discovered I had hardware problems with that - the company has now replaced my e-reader and I am not having anymore issues