problem with abline and regression plot

[mboutsen]

I use 2.9.0
when using the following commands with the attached lbw.txt

lbw<-read.table("lbw.txt")
reg<-(lbw$PDBB~lbw$PDMR)
plot(lbw$PDMR,lbw$PDBB)
abline(reg)

I can't get the plot with the regression line

Error in int_abline(a = a, b = b, h = h, v = v, untf = untf, ...) :
plot.new has not been called yet.
And a blank plot appears. ...

What is strange is that the four following lines submitted together give a regression line but I get the same error if I submit these lines step by step

Is there a solution?

Thanks

mboutsen
statistician
brussels university