Trouble with Sweave and Beamer

Dear All,
I am running Debian testing on my box and I installed latex and R from
the standard repositories.
I am trying my hands at sweave, but somehow I am experiencing problems
(I am trying to use beamer and Sweave). Please see the snippet at the
end of the email and saved as report.Rnw.

When I run the command

$ R CMD Sweave report.Rnw
Writing to file report.tex
Processing code chunks ...
   1 : echo term verbatim

You can now run LaTeX on 'report.tex'

It looks like everything is ok, but when I pdflatex it, I get an error
(I am pasting only the end of the console output)


no file report.nav.
(/usr/share/texmf-texlive/tex/latex/ae/t1aett.fd)
Runaway argument?

  >  x<- rnorm(100)>  xm<- mean(x)>  xm \end {Sinput} \begin {Soutput}\ETC.

! Paragraph ended before \FV at BeginScanning was complete.
<to be read again>
                     \par
l.42 \end{frame}

?


Can anyone tell me what is going wrong?
Many thanks

Lorenzo


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass{beamer}

\usetheme{Darmstadt}
\usefonttheme[onlylarge]{structurebold}
\setbeamerfont*{frametitle}{size=\normalsize,series=\bfseries}
\setbeamertemplate{navigation symbols}{}


% Standard packages

\usepackage[english]{babel}
\usepackage[latin1]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{Sweave}


% The main document

\begin{document}


\setlength{\unitlength}{\textwidth}  % measure in textwidths


\begin{frame}[t]{Data Representation and Analysis}



<<echo=TRUE>>=
x<- rnorm(100)
xm<- mean(x)
xm
@



\end{frame}