GetScriptDescriptors not being called on Script Control

Question

Hi,

I'm building a script control for asp.net Ajax, and while i can get the GetScriptReferences() function to be called, i cannot get the GetScriptDescriptors().

I've tried deriving from ScriptControl, ScriptControlBase, IScriptControl. I'm registering the control with the pages script manager, but i still cannot get the function to be called?

Any ideas on what i might have missed?

public class FilterGroupingControl : CompositeControl, IScriptControl
{
    public List<FilterGrouping> Groupings { get; set; }

    public FilterGroupingControl()
    {
        this.Groupings = new List<FilterGrouping>();
    }

    protected override void OnPreRender(EventArgs e)
    {
        #region register control with script manager

        ScriptManager scriptManager = ScriptManager.GetCurrent(Page);
        if (scriptManager == null)
            throw new InvalidOperationException("There must be a script manager on the page");
        scriptManager.RegisterScriptControl(this);

        #endregion

        base.OnPreRender(e);
    }

    public IEnumerable<ScriptDescriptor> GetScriptDescriptors()
    {
        throw new InvalidOperationException();
        ScriptControlDescriptor d = new ScriptControlDescriptor("Web.UI.Controls.FilterGroupingControl", this.ClientID);
        d.AddProperty("Groupings", this.Groupings.ToArray());


        return new ScriptDescriptor[] { d };
    }


    public IEnumerable<ScriptReference> GetScriptReferences()
    {
       // throw new InvalidOperationException();
        return new ScriptReference[0];
    }
}