button click not working inside modal pop up

<asp:UpdatePanel runat="server" ID="u" UpdateMode="Always">
        <Triggers>
            <asp:AsyncPostBackTrigger ControlID="btnSend" EventName="Click" />
        </Triggers>
        <ContentTemplate>

            <asp:Panel runat="server" ID="popBooknow" class="pad1" BackColor="Black" Width="225px"
                Height="325px">
                <h3>
                    Express your interest</h3>
                <div class="row">
                    Name &nbsp;
                    <asp:TextBox runat="server" ID="txtName" class="input" Width="200px"></asp:TextBox>
                    <asp:RequiredFieldValidator runat="server" ID="rfv1" ControlToValidate="txtName"
                        ErrorMessage="*" ForeColor="Red" ValidationGroup="send"></asp:RequiredFieldValidator>
                </div>
                <br />
                <div class="row">
                    Phone &nbsp;
                    <asp:TextBox runat="server" ID="txtPhone" class="input" Width="200px"></asp:TextBox>
                    <asp:RequiredFieldValidator runat="server" ID="RequiredFieldValidator1" ControlToValidate="txtPhone"
                        ErrorMessage="*" ForeColor="Red" ValidationGroup="send"></asp:RequiredFieldValidator>
                </div>
                <br />
                <div class="row">
                    Email &nbsp;
                    <asp:TextBox runat="server" ID="txtEmail" class="input" Width="200px"></asp:TextBox>
                    <asp:RequiredFieldValidator runat="server" ID="RequiredFieldValidator2" ControlToValidate="txtEmail"
                        ErrorMessage="*" ForeColor="Red" ValidationGroup="send"></asp:RequiredFieldValidator>
                </div>
                <br />
                <asp:Button runat="server" ID="btnClose" Text="Close" CssClass="button" OnClick="btnClose_Click" />
                   <asp:Button runat="server" ID="btnSend" Text="Send" OnClick="btnSend_Click" CssClass="button" />
            </asp:Panel>

        </ContentTemplate>
    </asp:UpdatePanel>

     <ajax:ModalPopupExtender ID="MPE" runat="server" TargetControlID="btnSubmit" PopupControlID="popBooknow"
        BackgroundCssClass="modalBackground" DropShadow="true" CancelControlID="btnClose">
    </ajax:ModalPopupExtender>