I suppose your problem is to give a date type value as the Y-Axis scale. Not every chart tools will permit a non-numeric value at the axis.
You can try showing only the date part of the date value as the Y Axis scale.
BTW, which is the component you are using ? The one I usually use is Chart director from http://www.advsofteng.com
Could you please explain the nature of the graph so I may able to help you further.