Undefined control sequence error when using combine class

Question

I am trying to Combine (6) .tex documents into one document. Have tried several 'combine' templates but nothing works. This is my current main document attempt.

\documentclass[book]{combine}
\title{Pepperdine Papers on LTL}
\author{J. Stanley Warford, David Vega, Scott M. Staley}
\date{today}

\begin{document}
\pagestyle{combine}         % use the combine page style
\maketitle          % main title 
\tableofcontents        % main ToC 
\clearpage

\section{Editor’s introduction} 
Here is where the introduction will be written
\label{Introduction}            % into main ToC (section 1)


\begin{papers}
    \coltoctitle{A Calculational Deductive System for Linear Temporal Logic}
    \coltocauthor{J. Stanley Warford, David Vega, Scott M. Staley}
    \label{eds4ltl-paper-copy}
    \include{eds4ltl-paper-copy}     

    \coltoctitle{Vega Paper}
    \coltocauthor{J. Stanley Warford, David Vega, Scott M. Staley}
    \label{Vega-Paper-copyFontsChanged}
    \include{Vega-Paper-copyFontsChanged}
\end{papers}

\clearpage
\section{Acknowledgements}
Here is where the Acknowledgments and Prologue will be written.

\end{document}

Here is the current error code I am getting:

eds4ltl-paper-copy.tex 9 Undefined control sequence. \leqnomode ->\tagsleft@true l.9 \leqnomode

Any help would be greatly appreciated. thank you