Certain types of \glspl{command}, called \glspl*{fragile}, can
seriously mess things up when they are used in what is termed a
\emph{moving argument}. These types of
\gls{argument}
are generally those whose contents are copied to another part of the
document. For example, section headings appear at the start of a
section, but they can also appear in the table of contents. The
\glsi{footnote} command is a fragile command, so
\begin{alltt}\wrong
\glsni{section}\marg{A heading\glsni{footnote}\marg{with a footnote}}
\end{alltt}
will cause an error\faq{An extra `\rightbracesym'??}{extrabrace}.

If there is no other command to use in its place, you should
use \gls{protect} immediately before the
fragile command:
\begin{codeS}
\begin{alltt}
\glsni{section}\marg{A heading\glsni{protect}\glsni{footnote}\marg{with a footnote}}
\end{alltt}
\end{codeS}%
\faq{Footnotes in LaTeX section headings}{ftnsect}This, however, is
a contrived example, because it isn't a good idea to have a footnote
in a
section heading, as it will also end up in the table of contents,
and possibly in page headings.