Can you please try the below steps?
1) Rename the folder "My Digital Editions" under C:\Users\<USERNAME>\Documents\
2) Launch ADE
The folder wasn't located in my documents, I found it my computer's program files. I made the change and now the app will open BUT it prompts me to upgrade, I do and I get an error message reading:
"Adobe Digital Editions 4.0 has stopped working: A problem caused the program to stop working correctly. Windows will close the program and notify you if a solution is available"
I get the error message if I choose not to upgrade, too. In the past I've gotten this message (a lot) but it usually resolves itself after one or two tries, but this time it wont.
I have the same problem. The error message came after closing for the first time. Tried downloading an earlier version and the same error message after the first closure.