trouble using 2 plots on the same chart

[Pascal Duchatelle <pduchatelle yahoo fr>]

I wish to put 2 plots on the same chart: a vertical column (bars) and a lineplot. Basically the bar plot is a 
"histogram" and the line a fit to the data. Whatever the order in which I create both plots, once the second 
is created, the X axis still has the correct scale (say 0 to 120) but the bars are just shifted to the right 
between 0 and 40 (there are actually 40 bins/bars). This means that as long as only one plot is created the X 
axis is ok (correct scale).
Is there a way to circumvent this problem ? The strange thing is that when using a histogram plot (density; 
like I did before knowing it was not what I needed) together with a lineplot worked just fine i.e. both plots 
were superimposed.
Thanx for any help.
Pascal