I used to have a similar problem with the interior PDF, and was curious to know if a browser affected it. I don't know why, but when I went from Firefox to Chrome, it worked and uploaded fine.
This is an older thread, you may not receive a response, and could
be reviving an old thread. Please consider creating a new thread.
Kindle Forum
A forum community dedicated to Amazon Kindle owners, authors, and enthusiasts. Come join the discussion about publishing, audio, troubleshooting, models, styles, reviews, accessories, classifieds, and more!