[R] Problem with xyplot when creating a .png graphic

[Harald Hofmann]

Hello,
I have the following problem. I have created a couple of scripts to 
create .png graphic files from data plots, using the xyplot (lattice) 
command. When I refere to the script with source(""), the script will be 
red but there is no output file. The scripts work well with the regular 
plot command and produce a nice PNG file.
On the other hand if I entre the single commands
png("file", width= , height=, etc)

xyplot(x,y)

dev.off()

The file gets created. It just doesn't work from a source file, which 
puzzles me a bit.

I am using R 2.10.1 64bit on a MacbookPro

Thanks for your help

Harald