Opps, sorry about that. In my troubleshooting I must have the quotes there. Original line was:
Literal1.Text = FusionCharts.RenderChart("../FusionCharts/ZoomLine.swf", "", XmlStr, "chart1", "1000", "400", True, True)
which is the same as :
Literal1.Text = FusionCharts.RenderChart("../FusionCharts/ZoomLine.swf", "", XmlStr.ToString, "chart1", "1000", "400", True, True)
With this I don't get the "No data to display" message. I actually get nothing; no graph at all. Even with debug = true.