modalpopup extender not showing

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C#3.0

C#

I have set a modalpopup extender to display the item of a dropdowmlist in it.but upon clicking the button nothing is poping up..need help..
Asp:

<asp:Panel ID="Panel1" runat="server" CssClass="HellowWorldPopup" Width="320px" Style="display:none">
        <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
        <ContentTemplate>
        <asp:Button ID="Button1" runat="server" Style="display:none" />
        <asp:ModalPopupExtender ID="ModalPopupExtender1" runat="server"
           TargetControlID="Button1" PopupControlID="Panel1" CancelControlID="CancelButton">
        </asp:ModalPopupExtender>
        <asp:Label ID="Label2" runat="server" />
        <asp:Button ID="OkButton" runat="server" Text="Ok" CausesValidation="true" />&nbsp;
           <asp:Button ID="CancelButton" runat="server" Text="Cancel" CausesValidation="false" />
</ContentTemplate>
</asp:UpdatePanel>
    </asp:Panel>

5.Next the next page, placed a Button and a TextBox like this:

<asp:TextBox ID="MyTextBox" runat="server" />
<asp:Button ID="MyButton" runat="server" Text="Popup" OnClick="MyButton_OnClick" />

6.and in the code behind for the page, i placed the handler for MyButton:

protected void MyButton_OnClick(object sender, EventArgs e)
{
     Label1.Text = MyTextBox.Text;
     UpdatePanel1.Update();
     ModalPopupExtender1.Show();
}