Actually you can try this

<asp:DropDownList ID="ddl_ChartNames" runat="server" AutoPostBack="FALSE" />

            <igmisc:WebAsyncRefreshPanel ID="WebAsyncRefreshPanel1" runat="server" TriggerControlIDs="ddl_ChartNames">
                <igchart:UltraChart ID="chart_Main" runat="server" Visible="false" Width="100%">
                </igchart:UltraChart>
            </igmisc:WebAsyncRefreshPanel>

if this does not work, attach a client onchange event to drop down like this on server side

ddl_ChartNames.attributes.Add("onchange","ddl_ChartNameChange()");

now the JS function will be used to refresh the warp explicitly, onchange of the dropdown.

function ddl_ChartNameChange()

{ 

var warp = ig_getWebControlById('WebAsyncRefreshPanel1');

if(warp)

{

warp.refresh();

}

Praveen.

This is how I load charts on a server side:

 Protected Sub ddl_ChartNames_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddl_ChartNames.SelectedIndexChanged

        Trace.Write("Part_Graph.ascx:ddl_ChartNames_SelectedIndexChanged")
        ' Retrieve available charts
        Dim oPlugins As New ChartPlugin
        oCharts = oPlugins.LoadCharts(Me.Context.Items("g_Login_Org_Tp"), Me.Context.Items("g_Login_Org_Id"), Me.Context.Items("g_Login_Auth_Cd"))
        oPlugins = Nothing
        Call GenerateChart(oCharts(ddl_ChartNames.Items(ddl_ChartNames.SelectedIndex).Text))

    End Sub

 I mean, change in a drop down list does not load different chart.

 Thanks a lot Anand I've already tried that, but in that case nothing happens :-(.