R help - Mar 2005 - need help with plot.rpart and text.rpart

Hi,
   I am new to R and need help with rpart. I am trying to create a
classification tree using rpart. In order to plot the reults I use the
plot function and the text function to label the plot of the tree
dendrogram with text. The documentation of text.rpart says : "For the
"class" method, label="yval" results in the factor levels
being used,
"yprob" results in the probability of the winning factor level being
used, and 'specific yval level' results in the probability of that
factor level" .  However, neither the label="yprob" option nor
the
label='specific yval level'  option works for me. I have copied a
section of my code in order to include the error message.
> plot(fit)
> text(fit, label="yprob")
Error in text.rpart(fit, label = "yprob") : 
        Label must be a column label of the frame component of the tree

On inspecting fit$frame I noticed that neither "yprob" nor
'specific
yval level'  are included in the frame. I therefore even tried to
create these variable in the frame by using the following

fit$frame <- transform(fit$frame, newVar=fit$frame$yval2[,4])

where fit$frame$yval2[,4] are the probabilities of the winning factor level.

However, using this I just get the values of "yval" as the labels
which I could have got anyway by setting the option label="yval".

I would really appreciate any help on this.
Thanks in advance.

Pat