Error: Measure becomes a series in the chart

[amic1]

hay,

I have a combination chart with a set of 2 series, S1 & S2 integrated.
I have a measure M and categories.
The problem is that the bars in the chart represents not only the set of series, but also the measure. you can actually see the name of the measure in the legends.
The bar that reflects the measure sums the numbers appears in the 2 series for each category.

Can anybody think for the cause of that?

Thanks,