}'??} 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 \protection is not the
answer;
Footnotes in LaTeX section headings
deals specifically with this case.