Delegate with a programmatically added usercontrol

Hello,
I have a problem with a delegate sub in my programmatically addeds usercontrol.
Let me explain:
First I added the usercontrol to the page and assign the delegate:
<%@ Reference Control="~/WebApplicatie/UserControls/Relatie_AangepasteGegevens.ascx" %>
hdrCtl = LoadControl("~/WebApplicatie/UserControls/Relatie_AangepasteGegevens.ascx")
UpdatePanel_Aangepaste_NAW_Gegevens.Controls.Add(hdrCtl)

 
DirectCast(hdrCtl, NAWGegevensAangepast).PageFunction_ToolboxInstellen = AddressOf Toolbox_RelatieAanpassing
Next I add the delegate to the usercontrol:
Public Delegate Sub PageFunctionSignature_ToolboxInstellen(ByVal Boolean_Geselecteerd As Integer) Public PageFunction_ToolboxInstellen As PageFunctionSignature_ToolboxInstellen  When I call the delegate, the webapplication gives a error: "object not set to an instance of an obje ...