Excel 2007 : Chart - Y Axis won't display both rows of data

Hi, I am working on a pivot chart, and for whatever reason, on the Y axis, it will not display both rows of my data. For example:

on my Y axis:


15 min. period 15 min. period 15 min. period 15 min. period
2/13/2011 2/14/2011 <should be date> 2/16/2011

It's kind of hard to explain - I have uploaded an attachment. Could someone please help me out?

Thank you very much!