You’ve looked at your LaTeX source and there’s no sign of a misplaced } on the line in question.
Well, no: this is TeX’s cryptic way of hinting that you’ve put a fragile command in a moving argument.
For example, \footnote is fragile, and if we put that in the
moving argument of a \section command, as
\section{Mumble\footnote{I couldn't think of anything better}}
we get told
The same happens with captions (the following is a simplification of a comp.text.tex post):! Argument of \@sect has an extra }.
\caption{Energy: \[e=mc^2\]}
giving us the error message
The similar (but more sensible):! Argument of \@caption has an extra }.
\caption{Energy: \(e=mc^2\)}
is more tiresome, still: there’s no error when you first run the
job … but there is on the second pass, when the list of figures
(or tables) is generated, giving:
in the! LaTeX Error: Bad math environment delimiter.
\listoffigures processing.
The solution is usually to use a robust command in place of the one
you are using, or to force your command to be robust by prefixing it
with \protect, which in the \section case would show as
\section{Mumble\protect\footnote{I couldn't think of anything better}}
However, in both the \section case and the \caption case,
you can separate the moving argument, as in
\section[moving]{static}; this gives us another standard
route — simply to omit (or otherwise sanitise) the fragile command
in the moving argument. So, one might rewrite the \caption
example as:
\caption[Energy: (Einstein's equation)]{Energy: \(E=mc^2\)}
In practice, inserting mathematics in a moving argument has already
been addressed in LaTeX 2e by the robust command \ensuremath:
\caption{Energy: \ensuremath{E=mc^2}}
So: always look for alternatives to the \protect route.
Footnotes can be even more complex; “footnotes in LaTeX section headings” deals specifically with that issue.
This answer last edited: 2012-02-09
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