Hi Ken,
Yes I have. Your PC or Laptop (and therefore Calibre) is not picking up your Kindle Fire as an external/portable drive. Try a different USB port or a different USB/Micro USB cable. If that fails and if you can, try to connect the Kindle to another PC or Laptop to see if that will pick it up. You have to eliminate the possible problems in order to narrow it down to the one that you are experiencing. My best guess would be that you have a poor connection at the Kindle end, heavily used Micro USB portstend to only work when they want to.
If you google "Love My Kindle fire" you will be directed to a forum all about the Kindle Fire. It's free to join and then if you go to the "Tips & Tricks" section there a step by step tutorial on how to do the very thing you are asking about.