Show alert Messages using AjaxPopupEx. in asp.net using jquery

//Modalpopup

<asp:ModalPopupExtender ID="ModalAlert" runat="server" TargetControlID="hdn_alertmodal" BehaviorID="ModalAlertB"

                PopupControlID="pnl_alert" CancelControlID="btn_cancelalert" BackgroundCssClass="modalBackground">

            </asp:ModalPopupExtender>

//Panel

<asp:HiddenField ID="hdn_alertmodal" runat="server" />

            <asp:Panel ID="pnl_alert" runat="server" Style="display: none;" class="modalPopup"

                Width="345px">

                <div style="padding: 0 0 10px 0;">

                    <div class="header">

                        Alert !</div>

                    <div style="width: 332px; text-align: center" class="body">

                        <div style="width: 100%; height: 8px;">

                        </div>

                        <asp:Label ID="lbl_messages" runat="server" CssClass="LabelHeader" Font-Bold="True"

                            Font-Size="11pt" Width="316px"></asp:Label>

                    </div>

                    <div style="text-align: center;">

                        <asp:Button ID="btn_cancelalert" runat="server" CssClass="myButton" Text="  OK  "

                            Width="74px" /></div>

                </div>

                <div class="footerCategory" align="right">

                </div>

            </asp:Panel>

////////////////Script

<script type="text/javascript">

$('#<%=lbl_messages.ClientID%>').html("To date must be grater than From Date"); 

$find('ModalAlertB').show();

return false;

                    

</script>