I've used ADE 4.0.1 several times and it has worked off and on. Sometimes it crashes when I add a book from the library and sometimes it crashes when I try to transfer to my kobo. It sometimes works properly as well. After trying several times, and re-installing the program, with one book that wouldn't transfer without crashing the program, I deleted ADE and install version 3.0. Now it works just fine. Why is this? I have a Mac with the most up to date OS.
It will be really helpful if you could share the crash logs with us.
You can find crashlogs in "Console" app.
In Console App, you need to click on the "User Diagnostic Reports" in the left sidebar and then there you will find report for ADE (something like "Adobe Digital Editions_<date>_<machine-name>.crash".