Error 1 (driver return code) -- Works on old computer but not new one

Ulrike Fischer above got me on the right track with more detailed output logging, thanks!

...If this isn't the source of the problem run on a command line xelatex --no-pdf file and xdvipdfmx -vv file to get a better error message.

Running xelatex --no-pdf test.tex completed fine with no errors

Running xdvipdfmx -vv test.xdv returned the following error:

xdvipdfmx:warning: Invalid CMap
xdvipdfmx:fatal: pdf_ref_obj(): passed invalid object.
Output file removed.

I was able to trace it down to an issue with the FontAwesome. If I remove the glyph it compiles fine. I was able to correct it with the following two lines added (I have them commented)

\documentclass{article}

\RequirePackage{xcolor}
\definecolor{customgold}{HTML}{D6BC55}

% Why do I need this one some computers and not others?
\usepackage{fontspec} % Was able to fix it with this line
\defaultfontfeatures{Extension = .otf} % ...and this line

\usepackage{fontawesome}
\newfontfamily{\FA}[Color=customgold]{FontAwesome}

\begin{document}

    \title{Fun with \LaTeX{}} \author{Author}

    \maketitle

    \section{Introduction} Introductions aren't important.

    \section{Conclusion} Sad conclusion... {\FA \faUniversity}

\end{document}

I just remembered: I added some time ago this in my the UserData-texmf tree in ...\fontconfig\config\localfonts2.conf

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
 <selectfont>
    <rejectfont>
      <glob>D:/MiKTeX2.9/fonts/type1/public/fontawesome/*</glob>
    </rejectfont>
 </selectfont>

<!-- REMOVE THIS LINE
<dir>Your font directory here</dir>
<dir>Your font directory here</dir>
<dir>Your font directory here</dir>
     REMOVE THIS LINE -->
</fontconfig>

This should avoid that xetex finds the type1 version of the font (which it shouldn't).