Have you tried changing your source from Amazon to Goodreads?
Amazon no longer works.
Quoted from an email sent by developer:
It's Max from Bolide Software.
I hope you are fine! I have some news about All My Books and Amazon.
Important news about Amazon as the book details source
So, Amazon turned off their old API, and all All My Books versions, including 5.0, cannot get book details from Amazon now. Of course, Amazon released a new API, and we published All My Books 5.1, but... I advise you to switch to Goodreads as the book details source. The problem with the new Amazon API is that it is even more limited now. Additionally to the requests limit, they are not returning the book synopsis now! All My Books 5.1 tries to get the synopsis on Goodreads by ISBN he gets on Amazon, but... Amazon looks not good now. We are looking for new good sources of the book details with the open API now. Goodreads is great, but mostly for American books.