We have been experiencing a problem where if the last category in a chart has no value for the series then the category is not plotted.
I have attached a simple webpage default.aspx and it's code behind.
There is also a AsposeFunctions.vb that has a couple of functions for populating a chart.
I have attached a sample template, a sample output (MissingTest.pptx)
After running the code
You will notice there is no category for Year 2012
If you then right click and select "Edt Data" and then close the excel without making a change the chart is now correct.