Book Error: Couldn't update this book, because it contains no openable non-generated files.
Hi FrameMaker friends:
Can anyone offer some clarity on this Book error message? 
The book and the generated files update as expected as long as all the files are open. I can't find any issues with the four generated files (TOC, LOF, LOT and LOP) and the nongenerated files seem fine, too. The book was created years ago and has been updated in the various versions over the years.
As I continue think about it, I did see missing fonts appear in the book window error report once. Is this an obscure way of telling us to uncheck ‘Remember Missing Fonts’ in Preferences?
Thanks in advance,
~Barb

