calling a user control which has update panel

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C#

ASP

user-controls

Hey Guys, I have this problem, here it is,
I'm calling a user control programatically

<pre>            using (Page page = new Page())
            {
                HtmlForm form = new HtmlForm();
                UserControl userControl = (UserControl)page.LoadControl("/UserControls/Products/ProductList.ascx");

                (userControl as BioPack.UserControls.Products.ProductList).initial(id);

                form.Controls.Add(userControl);
                using (StringWriter writer = new StringWriter())
                {
                    page.Controls.Add(form);
                    HttpContext.Current.Server.Execute(page, writer, false);
                    return writer.ToString();
                }
            }

Here's my user control

<asp:DataList ID="DataListProductList" runat="server" RepeatColumns="4" Visible="false"
    Style="margin-right: 10px; height: auto;" OnItemDataBound="DataListProductList_ItemDataBound" OnItemCommand="DataListProductList_ItemCommand">
    <ItemTemplate>
        <div class="CategoryBox" style="removed: pointer; color: white; font-weight: bold; text-align: center">
            <asp:HiddenField ID="HiddenFieldID" Value='<%# Eval("pId") %>' runat="server"></asp:HiddenField>
            <asp:ImageButton ID="ImageProductMainButton" CssClass="ProductPicture" CommandName="LoadInfo" CommandArgument='<%# Eval("pId") %>' runat="server" />
            <div class="CategoryBoxText">
                <asp:Label Text='<%# Eval("pName") %>' runat="server" ID="LabelCategoryName" />
            </div>
        </div>
        <br />
    </ItemTemplate>
</asp:DataList>

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <asp:Panel ID="PanelProductInfo" runat="server" Visible="false">
            <asp:Label ID="LabelProductInfo" runat="server" ForeColor="White" />
        </asp:Panel>
    </ContentTemplate>
</asp:UpdatePanel>

The problem is the update panel, without it it works fine, but when I include it, I get this error, please help me out

Error executing child request for handler 'System.Web.UI.Page'.