Using multiple Ajax ModalPopupExtender on same page in ASP.Net

How to use two model popup Extender on same page

on New button it is opening but on Credit button it is not opening popup window.

<asp:Button ID="btn_New" runat="server"  Text="New" Width="74px" OnClick="btn_New_Click" />     
<cc1:modalpopupextender ID="mp1" runat="server"  PopupControlID="Panl3" TargetControlID="btn_New" CancelControlID="btn_close" BackgroundCssClass="Background"> </cc1:modalpopupextender>                        
<asp:Panel ID="Panl3" runat="server" CssClass="Popup" align="left" style = "display:none">
    <asp:Button ID="Button2" runat="server" Text="Close" />
    <iframe  style=" width: 980px; height: 750px;" id="irm1" src="partypy2.aspx" runat="server"></iframe>
    <br/>
</asp:Panel>
                                       
<asp:Button ID="btn_CR" runat="server"  Text="Credit" Width="74px" OnClick="btn_CR_Click" />  
<cc1:modalpopupextender ID="mp2" runat="server"  PopupControlID="Panl4" TargetControlID="btn_CR" CancelControlID="btn_close" 
    BackgroundCssClass="Background"> </cc1:modalpopupextender>                        
<asp:Panel ID="Panl4" runat="server" CssClass="Popup" align="left" style = "display:none">
    <asp:Button ID="Button1" runat="server" Text="Close" />
    <iframe  style=" width: 980px; height: 750px;" id="Iframe1" src="partycrdt.aspx" runat="server"></iframe>
    <br/>
</asp:Panel>