Beamer file that was working is now failing at line 1

Question

I had an old presentation in beamer that I wanted to update. It worked previously, but now, when I run it, I get an error:

!Undefined control sequence.
1.1 \beamer@endinputifotherversion

Here is a minimal example

\documentclass{beamer} {
  \mode<presentation> {
  %\usetheme{Goettingen}
  % or ...

  \setbeamercovered{transparent}
  % or whatever (possibly just delete it)
  \usecolortheme{albatross}
  \usecolortheme{sidebartab}
}

\usepackage{natbib}
\usepackage[english]{babel}
% or whatever

\usepackage[latin1]{inputenc}
% or whatever

\usepackage{booktabs}
\usepackage{listings}
\usepackage{times}
\usepackage[T1]{fontenc}
% Or whatever. Note that the encoding and the font should match. If T1
% does not look nice, try deleting the line with the fontenc.

\usepackage{listings}
\usepackage{url}
\lstloadlanguages{SAS} \lstset{language = SAS}


\setbeamercolor{navigation symbols}{fg = white, bg = white}
\setbeamercolor{sectionintoc}{fg = white}

\title[PROC LOGISTIC: Traps for the unwary] % (optional, use only with long paper titles)
{PROC LOGISTIC: Traps for the unwary}


\author{Peter L. Flom}
% - Use the \inst{?} command only if the authors have different
%   affiliation.

\institute[Peter Flom Consulting] % (optional, but mostly needed)
{Peter Flom Consulting}

\date[Short Occasion] % (optional)
{NESUG\\
September, 2008}

\subject{Talks}
% This is only inserted into the PDF information catalog. Can be left
% out.

\AtBeginSection[] {
 \begin{frame}<beamer>
    \frametitle{Outline}
    \tableofcontents[currentsection]
  \end{frame}
 }


% If you wish to uncover everything in a step-wise fashion, uncomment
% the following command:

%\beamerdefaultoverlayspecification{<+->}


\begin{document}
\begin{frame}
  \titlepage
\end{frame}

\begin{frame}
  \frametitle{Outline}
  \tableofcontents[pausesections]
  % You might wish to add the option [pausesections]
\end{frame}


\section{Introduction}
\begin{frame}
\frametitle{Introduction - 1}
\begin{itemize}
\item  This paper covers some `gotchas' in
SAS\textsuperscript\textregistered\ PROC LOGISTIC.
\item  A `gotcha' is a mistake where the program runs, there
may be a note or a warning, but no errors.
\item  Output appears. But it's the wrong output.
\item  Not a primer on PROC LOGISTIC, nor on logistic regression.
\end{itemize}
\end{frame}

\begin{frame}
\frametitle{Introduction - 2}
Each section has several subsections.
\begin{enumerate}
\item The `gotcha'.
\item An example.
\item Evidence you have that it occurs.
\item How to fix it  --- sometimes with references
\item Explanation (where needed)
\end{enumerate}
\end{frame}

\end{document}

I have no clue what is wrong here.