Originally Posted by Blossom
There's no choose application option.
This means some other App is trying to open the file by default instead of the Kindle Reader App. Check post # 82 in this thread.
Whenever you find the offending App and clear the Launch By Default you will receive this message when opening a file. I believe SCION never checked the Use by default for this action when opening the file and receiving the Complete action using pop-up. There is a check mark box on this pop-up and checking it will always cause the Fire to try and open a particular file with whatever App you may have told it to. For example, if you use Mantano for PDF by default it could be interfering with the Kindle Reader App which I believe will also open PDFs on the Fire.