After Build, I saw 3 warnings.
The key warning was:
" Hyperlink not resolved: C:\Users\Max\Documents\My Dropbox\00 TNB\02 TNB ebook\00pbs\book.html"
I removed the path and left only book.html#toc
That solved the problem and voila! on hour 10 of fighting with the problem it is solved. I will post the complete workflow in a separate message.