Hi,
Please make sure you have graph structure as below,
<asp:chart id="chart1" runat="server" xmlns:asp="#unknown">
<series>
<asp:series name="series1">
</asp:series>
</series>
</asp:chart>
Error says that you are missing Series with the given name.
[Edit]
Let me know if this is in ASP.NET or in C# windows forms ?
[/Edit]
Best luck
~Amit