exporting to beamer error: "org-beamer--normalize-argument: Wrong type argument: stringp, nil"

[Rob Stewart <robstewart57@gmail.com>]

Hi,

 I have followed this tutorial to export from org to beamer frames.
http://orgmode.org/worg/exporters/beamer/ox-beamer.html .
Unfortunately, the frames are not created for 2nd level headings.
Instead, subsections are used. I am using org-mode from the git
repository, pulled today using commit f871fb6 . I have tried both
org-export-to-pdf and org-beamer-export-to-pdf . The first is not
effective (LaTeX output below). The latter throws an error
"org-beamer--normalize-argument: Wrong type argument: stringp, nil" .

%% ORG FILE %
#+TITLE: Example Presentation
#+AUTHOR: Joe Bloggs
#+LATEX_CLASS: beamer
#+LATEX_CLASS_OPTIONS: [presentation]
#+BEAMER_THEME: Madrid
#+OPTIONS: H:2

* First Section

** Frame 1

** Frame 2
%%%

STEP 2: M-x org-export-to-pdf

%% GENERATES %%
% Created 2013-10-02 Wed 23:24
\documentclass[presentation]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{fixltx2e}
\usepackage{graphicx}
\usepackage{longtable}
\usepackage{float}
\usepackage{wrapfig}
\usepackage{rotating}
\usepackage[normalem]{ulem}
\usepackage{amsmath}
\usepackage{textcomp}
\usepackage{marvosym}
\usepackage{wasysym}
\usepackage{amssymb}
\usepackage{hyperref}
\tolerance=1000
\author{Joe Bloggs}
\date{\today}
\title{Example Presentation}
\hypersetup{
  pdfkeywords={},
  pdfsubject={},
  pdfcreator={Emacs 24.3.1 (Org mode 8.2.1)}}
\begin{document}

\maketitle
\tableofcontents


\section{First Section}
\label{sec-1}

\subsection{Frame 1}
\label{sec-1-1}

\subsection{Frame 2}
\label{sec-1-2}
% Emacs 24.3.1 (Org mode 8.2.1)
\end{document}
%%%