Unfortunately Adobe doesn't have any interest in proper support for Digital Editions (or if it does, it keeps it well hidden).
Do you rely on ADE2.0, or can you just revert to ADE1.7.2?
That is what I have done; in my case because of a bug with ADE2.0 relating to Sony PRS-350 and Overdrive use,
but there are lots of other bugs in ADE2.0 as well; many of which can be fixed.by moving to 1.7.2.
I realize this is slightly more difficult to explain to your customers as it doesn't come up automatically on the Adobe site,
but probably much simpler than trying to work through the myriad problems with ADE2.0.
The Adobe DRM ADEPT infrastructure should be designed for people not used to computers;
but it is hostile to such people even when it works properly, and a complete menace when it doesn't.
I really respect the librarians who have the task of helping these users.
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
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