[R] Issues with Sweave and inclusion of graphics from nlme

[caroline.truntzer at chu-lyon.fr]

Dear all,
I'm using the nlme package. I would like to introduce the plot of my
groupedData object in my latex report using Sweave but it doesn't work. 
I have no error message in R (Sweave(my.file_Rnw)) and the plot is
generated in R, but when I want to see the pdf (I'm using TexnicCenter) of
my report, there is an error message and no pdf file is generated. It seems
that the plot generated by plot.nmGroupedData is not found by TexnicCenter.
Does anyone have an idea on how to solve this problem?
Thank you,
Caroline