When I try to transfer a book to my Kindle Fire from Calibre and go to open it, the message states it is not the correct format and that I must delete it?? These are books I purchased on Amazon and transferred to my Kindle for Mac, which I then transferred to Calibre. Why can't I transfer the books to my Kindle Fire? I know I can do it through Amazon-Manage My Kindle, but the purpose of having Calibre (for me) is to have a backup of all my Amazon books in case something should happen to them on Amazon and I can retrieve them and read them on my Kindle.
Help!!
Paulette