[XeTeX] error \begin{document}

[Ruth Robbins]

Here's everything up until the error message

% !TEX encoding = UTF-8 Unicode
% !TEX TS-program = XeLaTeX
% XeLaTeX can use any Mac OS X font. See the setromanfont command below.
% Input to XeLaTeX is full Unicode, so Unicode characters can be typed  
directly into the source.

% The next lines tell TeXShop to typeset with xelatex, and to open and  
save the source with Unicode encoding.
\documentclass[12pt]{book}
\usepackage{geometry}                % See geometry.pdf to learn the  
layout options. There are lots.

\geometry{letterpaper}                   % ... or a4paper or a5paper  
or ...
%\geometry{landscape}                % Activate for for rotated page  
geometry
%\usepackage[parfill]{parskip}    % Activate to begin paragraphs with  
an empty line rather than an indent

\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{longtable}

% Will Robertson's fontspec.sty can be used to simplify font choices.
% To experiment, open /Applications/Font Book to examine the fonts  
provided on Mac OS X,
% and change "Hoefler Text" to any of these choices.

\usepackage{fontspec,xltxtra,xunicode}
\defaultfontfeatures{Mapping=tex-text}
\setromanfont[Mapping=tex-text]{Charis SIL}
\setsansfont[Scale=MatchLowercase,Mapping=tex-text]{Charis SIL}
\setmonofont[Scale=MatchLowercase]{Charis SIL}

\title{ESQUISSE PHONOLOGIQUE ET GRAMMATICALE D’UN
PARLER SÉNOUFO:\\
LE TYÉBARA DE KORHOGO
CÔTE D’IVOIRE}
\author{Elizabeth Mills}
\date{}    % Activate to display a given date or no date
\begin{document}