[R] Sweave question

[Rafael A. Irizarry]

Using Sweave in the tools library (R version 1.8.0: sorry i havent 
upgraded), it seems i cant use if statements in R chunks that make graphs. 
i have this:

<<fig=TRUE,echo=F>>=
par(mfrow=c(1,1))
if(exists("x")) 
	plot(x,x)
else{
  plot(1,1,type="n")
  text(1,1,"data not available.\n")
}
@

and I get this error:

Error:  chunk 6
Error in parse(file, n, text, prompt) : parse error

any help is appreciated.

thanks and apologies if this not a problem in R 1.8.1
rafael