I have bought a number of e-books from you. As a Kindle user I am mainly interested in the mobi versions, and it has worked fine to upload them to my documents in Amazon. However, a few days ago I purchased and downloaded 'Exploring Arduino' by Jeremy Blum from your site. It is not accepted by Amazon as a valid mobi file. If I copy it by USB to my Kindle it can't be opened as a valid file, nor by the Kindle reader for PC. When trying to open the file in another reader (Moon + Reader Pro for Android) the reader crashes.
All other mobi files produced by you have worked fine in the above cases.
So, I suggest you take a look at regenerating and validating the mobi file for this book.
I'd be happy to help. From what I understand we have fixed the mobi file for this title. Exploring Arduino is now bigger than the 50MB limit that Amazon has regarding sending it to Kindle.
Instead, you can transfer larger ebooks to your Kindle by downloading them to your computer, connecting your Kindle to your computer with a USB cord, and moving the file into the Kindle's documents folder. Let us know if you have questions, and you can find more information on Amazon's help page.
I hope this helps!
Customer Service Representative