### An extra '`}`'??

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

      ! Argument of \@sect has an extra }.

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 above case would show as

      \section{Mumble\protect\footnote{%
          I couldn't think of anything better}}

Note that, in some cases, simple `\protect`ion is not the answer; Footnotes in LaTeX section headings deals specifically with this case.