I am running Windows 8.1 and Adobe Digital Editions crashes with a null reference error. I have books I need to access I purchased during the summer/fall of 2013. I had this working on Windows 8. I am sick to death of the DRM crap THAT IS CONSTANTLY BREAKING that is being foisted on consumers.
DRM is bad enough at the best of times, but a second rate infrastructure and third rate software (ADE2) certainly make it worse.
You may find v1.7.2 works for you.
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
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
Some people have found ADE trying to upgrade automatically.
It appears (not 100% sure) that if you install ADE2.0 as a new install (not as an upgrade) that your 1.7.2 will continue to run.
Probably best to say no if 2.0.x installation asks if you want to migrate your library.