模板中所有出现的“\section\subsection...”都会报告以下错误“未定义的控制序列。\section{Introduction}”

Question

这是我使用的模板下载链接。模板下载链接 当我取消注释模板中的“\section”时，会报一些错误。

\documentclass[jcs]{iosart2x}

\pubyear{0000}
\volume{0}
\firstpage{1}
\lastpage{1}

\begin{document}

\begin{frontmatter}

%\pretitle{}
\title{Article Title}
\runningtitle{Article Title}
%\subtitle{}

% Two or more authors:
\author[A]{\inits{N.}\fnms{Name1} \snm{Surname1}\ead[label=e1]{[email protected]}%
\thanks{Corresponding author. \printead{e1}.}},
\author[B]{\inits{N.N.}\fnms{Name2 Name2} \snm{Surname2}\ead[label=e2]{[email protected]}}
and
\author[B]{\inits{N.-N.}\fnms{Name3-Name3} \snm{Surname3}\ead[label=e3]{[email protected]}}
\runningauthor{N. Surname1 et al.}
\address[A]{Department first, \orgname{University or Company name},
Abbreviate US states, \cny{Country}\printead[presep={\\}]{e1}}
\address[B]{Department first, \orgname{University or Company name},
Abbreviate US states, \cny{Country}\printead[presep={\\}]{e2,e3}}

\begin{abstract}
Abstract text.
\end{abstract}

\begin{keyword}
\kwd{Keyword one}
\kwd{keyword two}
\end{keyword}

\end{frontmatter}

\section{}\label{s1}

\subsection{}\label{s1.1}

错误信息如下：

Undefined control sequence. \section{}
Undefined control sequence. \subsection{}
Undefined control sequence. \begin{thebibliography}{5}
Missing number, treated as zero. \begin{thebibliography}{5}

日志信息：

\c@sv@footnote=\count309
! Undefined control sequence.
\Sectionformat #1#2->\ios@Sectionformat 
                                        {#1\@nameuse {ios@section@level@\ios...
l.60 \section{}
               \label{s1}