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