My Code is:
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:Button ID="Button1" runat="server" Text="Button" />
<asp:Panel ID="Panel1" CssClass="modalPopup" runat="server">
<div id="modal" runat="server">
<asp:TextBox ID="TextBox1" runat="server" Visible="true"></asp:TextBox>
<cc1:NumericUpDownExtender ID="NumericUpDownExtender1" TargetControlID="TextBox1" Minimum="1"
runat="server">
</cc1:NumericUpDownExtender>
</div>
</asp:Panel>
<cc1:ModalPopupExtender ID="ModalPopupExtender1" PopupDragHandleControlID="modal"
BackgroundCssClass="modalBackground" TargetControlID="Button1" PopupControlID="Panel1"
runat="server">
</cc1:ModalPopupExtender>
</form>
</body>
Here, modal popup was not showing my numeric updown extender, i dont know what was the issue here.FYI: Im running my code in IE8.