I looked through all of these issues and nothing assisted in my resolution. My ADEv2.x was working...then all of a sudden decided to stop working. Nice.....
I started tracing / tracking what files were being utilized and/or starting and quickly figured something out.
There is a file called "user.config" and was located..on my machine...here:
C:\Users\Administrator\AppData\Local\Adobe_Systems_Incorporate\Digital Editions.exe_Url_oxhkcwg4hiitguzc245j2ayi3d0zprco\2.0.0.0
My file was zero bytes.
I installed ADE on another system, copied this file from my VM to my machine and TaDAAAA...problem resolved!!!
Hope this helps others as it is another alternative.