Can someone lend me a hand with a weird problem I'm having with a stacked column chart I've generated?

http://i43.tinypic.com/10hoemq.jpg

I'm trying to show the count of rows found for each of the elements in the series, grouped by date, showing the last 7 days. The legend shows me that the series are being identified correctly and given a unique color, and I see that the row counts are represented by proportionally correctly color columns.. but the columns seem to be "floating".

The "categories" fields are the past 7 days, each having thier own column. The problem is that if there is data for one of the elements, that data is not resting on the very bottom of the chart along the X axis.. it is floating. How do I make all of the data rest on the X axis?