菜鸟问题，关于ascx中加入textbox出现的问题

通过这段在页面中插入ascx。
 $.ajax({
                            type: "POST", //POST
                            url: "GridViewDrillDownjQueryAjax.aspx/GetOrders", //Set call to Page Method
                            data: params, // Set Method Params
                            beforeSend: function(xhr) {
                                xhr.setRequestHeader("Content-type", "application/json; charset=utf-8");},
                            contentType: "application/json; charset=utf-8", //Set Content-Type
                            dataType: "json", // Set return Data Type
                            success: function(msg, status) {
                                $('#progress').css('visibility','hidden');
                                $(master).children()[0].src = src;
                                $(detail).html(msg);
                                $(detail).slideToggle("normal"); // Succes Callback
                                },
                            error: function(xhr,msg,e){
                                alert(msg);//Error Callback
                                }
                            });然后ascx的源码是
<asp:SqlDataSource ID="sqlDsOrders" runat="server" ConnectionString="<%$ ConnectionStrings:Northwind %>"
    SelectCommand="SELECT [OrderID], [OrderDate], [RequiredDate], [Freight], [ShippedDate] FROM [Orders] WHERE ([CustomerID] = @CustomerID)">
    <SelectParameters>
        <asp:Parameter Name="CustomerID" Type="String" DefaultValue="" />
    </SelectParameters>
</asp:SqlDataSource>
<asp:Repeater ID="List" DataSourceID="sqlDsOrders" runat="server">
    <HeaderTemplate>
        <table class="grid" cellspacing="0" rules="all" border="1" style="border-collapse: collapse;">
            <tr>
                <th scope="col">&nbsp;</th>
                <th scope="col">Order ID</th>
                <th scope="col">Date Ordered</th>
                <th scope="col">Date Required</th>
                <th scope="col" style="text-align: right;">Freight</th>
                <th scope="col">Date Shipped</th>
            </tr>
    </HeaderTemplate>
    <ItemTemplate>
        <tr class='<%# (Container.ItemIndex%2==0) ? "row" : "altrow" %>'>
            <td class="rownum"><%# Container.ItemIndex+1 %></td>
            <td style="width: 80px;"><%# Eval("OrderID") %></td>
            <td style="width: 100px;"><%# Eval("OrderDate","{0:dd/MM/yyyy}") %></td>
            <td style="width: 110px;"><%# Eval("RequiredDate", "{0:dd/MM/yyyy}")%></td>
            <td style="width: 50px; text-align: right;"><%# Eval("Freight","{0:F2}") %></td>
            <td style="width: 100px;"><%# Eval("ShippedDate", "{0:dd/MM/yyyy}")%></td>
        </tr>
    </ItemTemplate>
    <FooterTemplate>
        </table>
    </FooterTemplate>
</asp:Repeater>gerorders函数如下
 public static string GetOrders(string customerId)
    {
        System.Threading.Thread.Sleep(500);
        Page page = new Page();
        CustomerOrders ctl = (CustomerOrders)page.LoadControl("CustomerOrders.ascx");
        ctl.CustomerId = customerId;
        page.Controls.Add(ctl);
        System.IO.StringWriter writer = new System.IO.StringWriter();
        HttpContext.Current.Server.Execute(page, writer, false);
        string output = writer.ToString();
        writer.Close();
        return output;
    }
我想在ascx中加入textbox控件和button。但一加入，ajax这段就会运行弹出出错提示的窗口。为什么。