I just had a similar experience & here's what I've done (no solution yet if ever). When I DLed the book to
K4PC it showed as a .azw type but when I DLed it to my computer for transfer to
Kindle, it showed as a .tpz file. This seems strange to me. Is it an AZW book or a TPZ book? Still investigating. Will DL directly to Kindle (once the battery is recharged), transfer to computer and see what it looks like.
Edit: The ebook brought in from the Kindle had the extension of .azw1. Apparently this is a Topaz ebook and skindle is not working with it. I had my doubts that it would work with a Topaz ebook but this is the first one I've bought to try it with. A .azw ebook purchased at the same time had no problem with skindle.