asp.net ModalPopupExtender not behaving properly - asp.net

Question

I have the following code on a .aspx file. If I comment out the ModalPopupExtender code works fine.:
<cc1:ModalPopupExtender BehaviorID="mdlPopup" runat="server" TargetControlID="btn"
ID="mdl1" PopupControlID="pnlPopup" OkControlID="LinkButton1" BackgroundCssClass="modalBackground" />
<asp:Panel ID="pnlPopup" runat="server" CssClass="confirm-dialog" Style="display: none;">
<div class="inner">
Work Order #: <asp:TextBox ID="txtWorkOrder" runat="server" Width="285" Text=""></asp:TextBox><br /><br />
Please Enter Corrective Actions<br />
<asp:TextBox ID="TextBox2" runat="server" Height="150" Width="285" TextMode="MultiLine"
Text=""></asp:TextBox>
<asp:Button ID="btnOK" runat="server" Font-Bold="true" Text="Submit" OnClick="click"
Width="150" />
<asp:LinkButton ID="LinkButton1" runat="server" CssClass="close" OnClick="cancel" />
</div>
</asp:Panel>
<asp:Button ID="btn" runat="server" Style="display: none;" />
<asp:Label ID="id" runat="server" Text="Label" Visible="false"></asp:Label>
The problem that I am having is that the page just hangs when I have this code in the .aspx file. Is there anything I should do. It does not even get to the Page_Load.
I am calling this page that has the above code with the following:
string url = "Alerts.aspx?";
url += "ID=" + id.Text;
Response.Redirect(url);