I am new to Beamer. When I run a sample code:
\begin{frame}
\begin{itemize}
\item Assuming equal power allocation at the source \vspace{0.2cm}
\item Water-filling scheme at the relays over spatial \& temporal domains \vspace{0.1cm}
\item IAPC at each relay puts a lid on the water vessel
\end{itemize}
\begin{columns}[2]
\column{0.4\textwidth}
\begin{itemize}
\item Relays are rarely used at very low \& high SNRs \vspace{0.2cm}
\item Stronger relay is used more often \vspace{0.2cm}
\end{itemize}
\column{0.6\textwidth}
\includegraphics[scale=0.4]{Figures/Pon/Pon_naf1_c.eps}
\end{columns}
\end{frame}
I get error: Package keyval Error: 2 undefined \end{frame}. Anyone know what's wrong?

[2]you don't need to tell beamer how many columns there are, it just sees the nested column environments (which should be environments, not commands) – David Carlisle Sep 01 '13 at 16:02