Error when producing multiple graphes

Dear all,

Within a larger script I use the following code to produce barplots for 
all variables contained in a dataframe "type3m":

    for(xn in names(type3m)) barplot(table(type3m[[xn]]), main = paste
    ("Barplot of", xn), width=0.75,legend.text=barnamesm,
    xlim=c(0,4),ylim=c(0,400))

The plots are produced and printed into a *.ps file. However, R gives an 
error message and aborts the script. The error message is:

    Fehler in rect(as.double(xleft), as.double(ybottom),
    as.double(xright),  :
            ung?ltiges erstes Argument

(it's in German. In English, it says something like "Error in 
rect(as.double(xleft), as.double(ybottom), as.double(xright),  : invalid 
first argument)

It seems to be some problem with the barplot function. The variables in 
the dataframe are discrete variables taking values from 1 to 4 (hence, 
the xlim=c(0,4) and the graph is supposed to show the frequency of each 
value. Maybe the problem is related to the fact that not some variables 
don't take all of the values, i.e., there are some that don't take the 
value 1, for example.

I spent quite some time trying to solve the problem, but can't manage 
it. What's wrong here and how can it be solved?

Thank you very much!

Uli


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