fontspec_error.tex

% Our tocloft configuration

\usepackage{tocloft}
\newlength{\mylen} %% extra space
\setlength{\mylen}{.2cm}
\addtolength{\cftsecnumwidth}{\mylen} % add the extra space after section numbers
\addtolength{\cftsubsecnumwidth}{\mylen} % add the extra space after subsection numbers

% How we load fontspec

\usepackage{fontspec}

% A sample TOC header

\chapter*{Authors' Notes}
\addcontentsline{toc}{chapter}{Authors' Notes}

% The error we get

xelatex -shell-escape screen.tex
This is XeTeX, Version 3.14159265-2.6-0.99996 (TeX Live 2016) (preloaded format=xelatex)
 \write18 enabled.
entering extended mode
(./screen.tex
LaTeX2e <2016/03/31>
Babel <3.9r> and hyphenation patterns for 22 language(s) loaded.
(./main.tex (/usr/local/texlive/2016basic/texmf-dist/tex/latex/base/book.cls
Document Class: book 2014/09/29 v1.4h Standard LaTeX document class
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/base/bk10.clo))
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/listings/listings.sty
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/listings/lstmisc.sty)
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/listings/listings.cfg))
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/fontspec/fontspec.sty
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/l3kernel/expl3.sty
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/l3kernel/expl3-code.tex)
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/l3kernel/l3xdvipdfmx.def))
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/l3packages/xparse/xparse.sty
)
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/fontspec/fontspec-xetex.sty
*************************************************
* fontspec warning: "tu-clash"
* 
* I have found the tuenc.def encoding definition file but the TU encoding is
* not defined by the LaTeX2e kernel; attempting to correct but you really
* should update to the latest version of LaTeX2e.
*************************************************
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/base/fontenc.sty
(/usr/local/texlive/2016basic/texmf-dist/tex/latex/base/tuenc.def
! Missing \endcsname inserted.
<to be read again> 
                   \def 
l.252 ...           \UnicodeEncodingName {}{"007E}
                                                  
? 

@mpacer, the font declaration causing the problem is:

\setsansfont [Path = fonts/,
    UprightFont = PTSansNarrow-Regular.ttf,
    BoldFont = OpenSans-Bold.ttf,
    ItalicFont = AvenirNextCondensed-Italic.ttf
 ]
{PTSansNarrow.ttf}

The font is stored in a fonts directory. It's also in my Mac's fontbook utility. Not sure if there's a conflict.

However, what've discovered though is that when I comment out this command, the book compiles without a problem. In the rendered book's section on typographical conventions, everything looks fine. HOORAY!

So I think the problem is resolved. However, since the book is 527 pages, it might be a while before we discover any problems.

Does get you a functional font declaration? My guess is that if you don't pass an explicit Extension parameter it defaults to Extension = .ttf which seems backwards for xelatex given it's otf support, but 🤷‍♀️.

\setsansfont [Path = fonts/,
Extension = .ttf,
UprightFont = PTSansNarrow-Regular,
BoldFont = OpenSans-Bold,
ItalicFont = AvenirNextCondensed-Italic
]
{PTSansNarrow}