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Using Emacs 21.2.1 and hyperlatex 2.7 and 2.8b the following
simple input file produces the error

Hyperlatex ERROR: (void-function incf)
right before \end{document}

\documentclass{article}
\usepackage{hyperlatex}
\usepackage{makeidx}
\input{/opt/hyperlatex/hlx/contrib/idxmods.hlx}

\T\begin{ifhtml}

\newcommand{\printindex}{%
\htmlonly{\HlxSection{-5}{}*{\indexname}\label{hlxindex}}%
\htmlprintindex}

\T\end{ifhtml}

\makeindex
\begin{document}

\title{Title}
\author{Author}
\maketitle

\section{Part 1} \index{Part!one}

\section{Part 2}\index{Part!two}

\printindex

\end{document}