Using multiple AJAX ModalPopupExtender in page using C# and VB.Net in ASP.Net

HiAwanish,

Check this example. Now please take its reference and correct your code.

HTML

<cc1:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</cc1:ToolkitScriptManager>
<asp:LinkButton ID="lnkDummy" runat="server"></asp:LinkButton>
<cc1:ModalPopupExtender ID="ModalPopupExtender1" BehaviorID="mpeAdd" runat="server"
    PopupControlID="pnlPopupAdd" TargetControlID="lnkDummy" BackgroundCssClass="modalBackground"
    CancelControlID="btnHideAdd">
</cc1:ModalPopupExtender>
<asp:Panel ID="pnlPopupAdd" runat="server" CssClass="modalPopup" Style="display: none">
    <div class="header">
        Modal Popup
    </div>
    <div class="body">
        This is add Modal Popup.
        <br />
        <asp:Button ID="btnHideAdd" runat="server" Text="Hide Modal Popup" />
    </div>
</asp:Panel>
<cc1:ModalPopupExtender ID="ModalPopupExtender2" BehaviorID="mpeUpdate" runat="server"
    PopupControlID="pnlPopupUpdate" TargetControlID="lnkDummy" BackgroundCssClass="modalBackground"
    CancelControlID="btnHideUpdate">
</cc1:ModalPopupExtender>
<asp:Panel ID="pnlPopupUpdate" runat="server" CssClass="modalPopup" Style="display: none">
    <div class="header">
        Modal Popup
    </div>
    <div class="body">
        This is update Modal Popup.
        <br />
        <asp:Button ID="btnHideUpdate" runat="server" Text="Hide Modal Popup" />
    </div>
</asp:Panel>
<asp:Button ID="btnAdd" Text="Add" runat="server" OnClick="Add" />
<asp:Button ID="btnUpdate" Text="Update" runat="server" OnClick="Update" />

Code

C#

protected void Add(object sender, EventArgs e)
{
    ModalPopupExtender1.Show();
}

protected void Update(object sender, EventArgs e)
{
    ModalPopupExtender2.Show();
}

VB.Net

Protected Sub Add(sender As Object, e As EventArgs)
    ModalPopupExtender1.Show()
End Sub

Protected Sub Update(sender As Object, e As EventArgs)
    ModalPopupExtender2.Show()
End Sub

Screenshot