# Meaning of fontspec related error

I've edited a document. The edited document works well on my system, but apparently reports this error on another system:

Undefined control sequence.
<argument> ...ontspec_tmp_int\endcsname 255*\real{0.5}\relax


The error appears when calling \maketitle which has been redefined to (not my doing):

\def\maketitle{
\thispagestyle{empty}
\vfill
\begin{raggedright}
\leavevmode
\vskip 1cm
\vskip 1cm
\normalfont
{\Huge {\textit{\@author}\par}}
\vfill
{\Large Name}
\newline
{\Large \href{mailto:name@name.edu}{name@name.edu}}
\newline
{\Large \href{http://name.com}{http://name.com}}
\newline
{\Large \@date\par}
\end{raggedright}
\null
\cleardoublepage
}

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Please reduce your document to a minimal working example (MWE) and edit it into your question. –  doncherry Mar 14 '12 at 0:20
@doncherry I am not able to do that, because I don't have access to the system with the error thrown to be able to reduce the document to only the non-functioning part. I only have the log file. –  ipavlic Mar 14 '12 at 0:21
Probably the other system is more up-to-date than yours. This is the same problem that caused me to be unable to compile the example in your previous question: Fontspec transparency problem. Try adding \usepackage{calc} to your preamble. –  Alan Munn Mar 14 '12 at 1:52
@Alan You are right. Can you please add your comment as an answer so that I can accept it? –  ipavlic Mar 14 '12 at 7:28

This error is due to changes in the LaTeX3 code that fontspec depends on. This code used to load the calc package, but no longer does, and fontspec hasn't yet reflected this change. The offending line of code is the \fontspec command, which sets the font opacity. You can solve the problem by adding.

\usepackage{calc}


to your preamble. It is likely that the this will be fixed relatively soon.

By the way, the offending line is not the way you should do this. In general, you should avoid using the \fontspec command to change fonts. Instead, you should define a new font family outside your title definition using e.g.

\newfontfamily\mytitlefont[Color=red,Opacity=0.5]{Adobe Garamond Pro}


and then inside your title redefinition use \mytitlefont.

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