[ESS] Problem with Sweave after upgarde to 13.05

[r]

Hi, my name is Riccardo, I use EMACS 23.1.1 and I have some trouble
after I upgrade ESS to the latest version (13.05). In particular I'm
having trouble working with .Rnw files because emacs is not able do
distinguish between ESS code and LaTeX code, and the major mode of the
buffer still remain in ESS mode and do not switch to LaTeX when I edit
the TeX code.  

I hope you can help me.

Best Regards, Riccardo