Private: Code & Script Snippet

try
{
ddl.SelectedValue = “value_from_db”;
ddl.DataSoure = myDataSource();
ddl.DataValueField = “value”;
ddl.DataTextField = “text”;
ddl.DataBind();
}
catch (ArgumentOutOfRangeException myException)
{
//exception will be caught if SelectedValue is not in the ddl
//no exception caught if SeletedValue is in the ddl
if (ddl.items.count > 0)
ddl.SelectIndex = -1;
}

Solution:

change:
<ajaxToolkit:ToolkitScriptManager ID=”ScriptManager1″ runat=”server” />
to:
<asp:ScriptManager ID=”ScriptManager1″ runat=”server” />