Pie charts and using the Y and X axis

I am having trouble with pie charts. My problem is that I do not seem to be able to select the Y or X axis. This has not been a issue for other chart styles. Does anyone know if this feature is not usable with pie charts? Or do I need to adjust options slightly?

      Thanks Simon

Pie Charts have only Y-Values which build the segments of the pie. There are NO X-values and no x-axis.