与 beamer 文档类别有关的问题

Question

我第一次尝试用 Latex 做演示。首先，我从 Wikipedia 复制了以下代码：

\documentclass[10pt]{beamer}
\title{Presentation on XXX topic}
\author{AAA}
\begin{document}
   \maketitle
    \begin{frame}
        \frametitle{This is the first slide}
        Here you can put any text/equation etc. 
        $a^2 + b^2 = c^2$.      
    \end{frame}
    \begin{frame}
        \frametitle{This is the second slide}
        \framesubtitle{A bit more information about this}
        Some random text.       
    \end{frame}
\end{document}

但是，我收到以下错误消息：

! Undefined control sequence.
l.2 \bbl@cs
           {beforestart}
? 
! Emergency stop.
l.2 \bbl@cs
           {beforestart}
End of file on the terminal!

我该如何解决这个问题？