[R] Problem with Sweave not recognising \Sexpr{}

[Mike White]

I am trying to run the Sweave example at 
http://www.stat.uni-muenchen.de/~leisch/Sweave/Sweave-Rnews-2002-3.pdf
However, the \Sexpr{} code is not being evaluated, although the actual R 
code within the {} runs ok in R.
Below is part of the resulting .tex file.  Can anyone help identify the 
cause? I am using R 2.10.1 on Windows XP.

Consider the \texttt{cats} regression example from Venables \& Ripley
(1997). The data frame contains measurements of heart and body weight
of \Sexpr{nrow(cats)} cats (\Sexpr{sum(cats$Sex=="F")} female,
\Sexpr{sum(cats$Sex=="M")} male).

Thanks
Mike White