When using msstackedcolumn2d and defining your dataset through the php class using createMSStDataset() and createMSStDataset() then the transformation to XML fails due to the seriesType being set to 2 instead of 4
Around line 1544, need to change
$this->chartSWF['msstackedcolumn2d'][1]=2;
to
$this->chartSWF['msstackedcolumn2d'][1]=4;
Then it works correctly.
Thanks