AJAX modalpopupextender not working.

<cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="btnShowPopup"
    PopupControlID="pnlpopup" CancelControlID="btnCancel" BackgroundCssClass="modalBackground">
</cc1:ModalPopupExtender>
<asp:Panel ID="pnlpopup" runat="server" BackColor="White" Width="400px" Style="display: none">
    <div class="inquery_area">
        <div class="inquery">
            <table style="width: 80%; margin: 0px auto;" class="table">
                <tr>
                    <td>
                        Name*
                       
                        <asp:TextBox ID="txtEnquireName" runat="server" placeholder="Type here"></asp:TextBox>
                    </td>
                </tr>
                <tr>
                    <td>
                        Email*
                      
                        <asp:TextBox ID="txtEnquireEmail" runat="server" placeholder="youremail@email.com"></asp:TextBox>
                    </td>
                </tr>
                <tr>
                    <td>
                        Mobile*
                     
                        <asp:TextBox ID="txtEnquirePhone" runat="server" placeholder="Phone or Mobile Number"
                            oncopy="return false" onpaste="return false" oncut="return false" onkeydown="return jsNumbers(event)"
                            MaxLength="10"></asp:TextBox>
                    </td>
                </tr>
                <tr>
                    <td>
                        Message*
                       
                        <asp:TextBox ID="txtEnquireMessage" runat="server" placeholder="Write your message"
                            TextMode="MultiLine" Height="100px"></asp:TextBox>
                    </td>
                </tr>
                <tr>
                    <td colspan="2" align="center">
                        <asp:Button ID="btnEnquireSubmit" runat="server" Text="submit" ValidationGroup="Enquire"
                            OnClick="btnEnquireSubmit_Click" />
                        <asp:Button ID="btnCancel" runat="server" Text="Cancel" CausesValidation="false" />
                        <asp:ValidationSummary ID="ValidationSummary2" runat="server" HeaderText="There were validation on the page: "
                            ShowMessageBox="true" DisplayMode="BulletList" ShowSummary="false" ValidationGroup="Enquire" />
                        <asp:HiddenField ID="HdPropertyId" runat="server" Value="0" />
                    </td>
                </tr>
            </table>
        </div>
    </div>
</asp:Panel>

<asp:LinkButton ID="lbEnquire" runat="server" CausesValidation="False" CommandName="Enquire"
                                                               CommandArgument='<%# Eval("Property_Id") %>' Text="ENQUIRE NOW" /></li>