I've just tried my sample code and it's working for me. What shapefile did you use? Try USA couties, in case you worked with different shapfile before. Try to exlude additional options, adding only 2 fields and SetPositions call.
one more question is how to set the pie value（percent） and label.
I just find a method to add the chart :
currently no labels for pie sectors are implemented. But it's possible to do. You can add enhancement request in Mantis in case you need such functionality.