"An error occurred while saving the book: an error occurred adding text and fonts to the book."
I am running Windows 10 (v10.0.17134); LR Classic CC v8.0 and v7.5 (to avoid yet another bug) both get the same error. i7-6700K with 16GB RAM, loads of free disk space, 15GB RAW cache, etc so no limitations that should cause problems. I have published around 15 books from LR on Blurb ever since the Book module first appeared; they all use the same layout standards and fonts so nothing new in this book.
The book was producing a PDF and also uploading to Blurb until I edited some text fields and expanded one text box. I have tried the community-selected workaround of selecting all text fields (Ctrl-Alt-A) and changing fonts to Arial then back to Myriad Pro (I have always used Myriad Pro except for Georgia on the cover) but still does not work. Tried both v8.0 and v7.5 but neither work. No text or image boxes added so can't have any new empty boxes (and I am pretty sure there never were any previously). No zero-sized photos or excessive padding on boxes.
After MANY hours of testing I found a fix, at least for my particular case. I can send a 2MB catalog with a reproducible error and a way of making it work, which also illustrates the bug of LR v8.0 not saving changes in the Book module.
I narrowed it down to a single line-and-a-bit of text in Myriad Pro; if this word-wraps to a second line in the paragraph then it will not produce a pdf unless I change font to Arial. If I remove a few letters so it doesn't word wrap, or put in a hard paragraph break at the end of the line instead of letting it word-wrap, then it will produce a pdf in Myriad Pro. Unfortunately if I add the paragraph break and change the first line to "Justify-last line justified" (so that it formats the same as if it did a word-wrap) then it won't generate a pdf; I need to make it "Justify-last line left" and add a short word to the sentence to make the line reach the right border and look the same as if the wordwrap was working.