As I can see from the code it is not only addRowData, but you use getRowData, humm both methods have a possibilty to add and get at once look here – (read carefull):
This is really starnge! Any other plugins and javascript libs? Also could you please try with just a grid in the page and only files for the grid? Also if everthing is ok, try step by step to include the other js fileas taht you use and etc. I think you understand may point
