Ciao a tutti
Sto utilizzando Metronic e la validazione di jquery presente in Metronic.
Utilizzo la versione 3.6.2. Ho questa codice:

codice:
<!DOCTYPE html>
<!--[if IE 8]> <html lang="en" class="ie8 no-js"> <![endif]-->
<!--[if IE 9]> <html lang="en" class="ie9 no-js"> <![endif]-->
<!--[if !IE]><!-->
<html lang="it" class="no-js" xmlns="http://www.w3.org/1999/xhtml">
<!--<![endif]-->
<!-- BEGIN HEAD -->
<head runat="server">
    <meta charset="utf-8" />
    <title>Scuolaecorsi</title>
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta content="width=device-width, initial-scale=1" name="viewport" />
    <meta content="" name="description" />
    <meta content="" name="author" />


    <!-- BEGIN GLOBAL MANDATORY STYLES -->
    <link href="http://fonts.googleapis.com/css?family=Open+Sans:400,300,600,700&subset=all" rel="stylesheet" type="text/css" />
    <link href="/Metronic/plugins/font-awesome/css/font-awesome.min.css" rel="stylesheet" type="text/css" />
    <link href="/Metronic/plugins/bootstrap/css/bootstrap.min.css" rel="stylesheet" type="text/css" />
    <link href="/Metronic/plugins/uniform/css/uniform.default.css" rel="stylesheet" type="text/css" />
    <link href="/Metronic/plugins/simple-line-icons/simple-line-icons.css" rel="stylesheet" />
    <link href="/Metronic/admin/layout/css/style.css" rel="stylesheet" />
    <link href="/Metronic/css/components.css" rel="stylesheet" type="text/css" />
    <!-- END GLOBAL MANDATORY STYLES -->


    <!-- BEGIN PAGE STYLES -->
    <link href="/Metronic/admin/pages/css/tasks.css" rel="stylesheet" type="text/css" />
    <!-- END PAGE STYLES -->


    <!-- BEGIN THEME STYLES -->
    <link href="/Metronic/admin/layout/css/custom.css" rel="stylesheet" />
    <link href="/Metronic/css/components.css" id="style_components" rel="stylesheet" type="text/css" />
    <link href="/Metronic/css/plugins.css" rel="stylesheet" type="text/css" />
    <link href="/Metronic/admin/layout/css/layout.css" rel="stylesheet" />


    <link href="/Metronic/admin/layout/css/themes/grey.css" rel="stylesheet" type="text/css" id="style_color" />
    <!-- END THEME STYLES -->


    <!-- BEGIN PAGE LEVEL STYLES -->
    <link rel="stylesheet" href="/Metronic/plugins/select2/select2.css" rel="stylesheet" />
    <link rel="stylesheet" type="text/css" href="/Metronic/plugins/bootstrap-fileinput/bootstrap-fileinput.css" />
    <link rel="stylesheet" type="text/css" href="/Metronic/plugins/bootstrap-wysihtml5/bootstrap-wysihtml5.css" />
    <link rel="stylesheet" type="text/css" href="/Metronic/plugins/bootstrap-datepicker/css/datepicker.css" />
    <!-- END PAGE LEVEL STYLES -->
</head>
<!-- END HEAD -->
<!-- BEGIN BODY -->
<body class="page-header-fixed page-quick-sidebar-over-content ">
    <form id="frmMaster" method="post" runat="server" enctype="multipart/form-data" class="form-data">
       <asp:LinkButton ID="btnSalva" CssClass="btn green" OnClick="Salva" runat="server">                            <i class="fa fa-check"></i>&nbsp&nbsp;Salva
                        </asp:LinkButton>


        <div id="dvError" class="alert alert-danger display-hide">
            <button class="close" data-close="alert"></button>


            <i class="fa fa-exclamation-circle"></i>
            <span></span>
        </div>


        <!--BEGIN TABS-->
        <div class="tabbable tabbable-custom tabbable-full-width">
            <ul class="nav nav-tabs">
                <li class="active">
                    <a href="#tab_1_1" data-toggle="tab"><i class="fa fa-cogs"></i>&nbsp;&nbsp;Anagrafica</a>
                </li>
            </ul>
            <div class="tab-content">


                <!--tab_1_1-->
                <div class="tab-pane active" id="tab_1_1">


                    <div class="portlet box">


                        <div class="portlet-body form">
                            <!-- BEGIN FORM-->
                            <div class="form-horizontal form-bordered" action="#">                               


                                <div class="form-group">
                                    <label class="col-sm-3 control-label">Denominazione centro*</label>
                                    <div class="col-sm-9">
                                        <asp:TextBox ID="txtDenominazione" CssClass="form-control denominazione" runat="server" TextMode="SingleLine"></asp:TextBox>
                                    </div>
                                </div>                              


                            </div>
                            <!-- END FORM-->
                        </div>
                    </div>




                </div>


            </div>
        </div>
        <!--END TABS-->


    </form>


    <!-- BEGIN JAVASCRIPTS(Load javascripts at bottom, this will reduce page load time) -->
    <!-- BEGIN CORE PLUGINS -->
    <!--[if lt IE 9]>
<script src="/Metronic/plugins/respond.min.js"></script>
<script src="/Metronic/plugins/excanvas.min.js"></script> 
<![endif]-->
    <script src="/Metronic/plugins/jquery.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/jquery-migrate.min.js" type="text/javascript"></script>
    <!-- IMPORTANT! Load jquery-ui-1.10.3.custom.min.js before bootstrap.min.js to fix bootstrap tooltip conflict with jquery ui tooltip -->
    <script src="/Metronic/plugins/jquery-ui/jquery-ui.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/bootstrap/js/bootstrap.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/bootstrap-hover-dropdown/bootstrap-hover-dropdown.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/jquery-slimscroll/jquery.slimscroll.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/jquery.blockui.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/jquery.cokie.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/uniform/jquery.uniform.min.js" type="text/javascript"></script>


    <!-- END CORE PLUGINS -->


    <!-- BEGIN JAVASCRIPTS(Load javascripts at bottom, this will reduce page load time) -->
    <!-- BEGIN PAGE LEVEL PLUGINS -->
    <script src="/Metronic/plugins/jquery-validation/js/jquery.validate.min.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/jquery-validation/js/localization/messages_it.js" type="text/javascript"></script>
    <script src="/Metronic/plugins/jquery-validation/js/additional-methods.min.js" type="text/javascript"></script>


    <script src="/Metronic/plugins/select2/select2.min.js" type="text/javascript"></script>
    <script type="text/javascript" src="/Metronic/plugins/bootstrap-fileinput/bootstrap-fileinput.js"></script>
    <script type="text/javascript" src="/Metronic/plugins/bootstrap-wysihtml5/wysihtml5-0.3.0.js"></script>
    <script type="text/javascript" src="/Metronic/plugins/bootstrap-wysihtml5/bootstrap-wysihtml5.js"></script>
    <script type="text/javascript" src="/Metronic/plugins/bootstrap-datepicker/js/bootstrap-datepicker.js"></script>
    <script type="text/javascript" src="/Metronic/plugins/bootstrap-datepicker/js/locales/bootstrap-datepicker.it.js"></script>


    <!-- END PAGE LEVEL PLUGINS -->


    <!-- BEGIN PAGE LEVEL SCRIPTS -->
    <script src="../../Js/centro.js"></script>
    <!-- END PAGE LEVEL SCRIPTS -->


    <!-- BEGIN PAGE LEVEL SCRIPTS -->
    <script src="/Metronic/scripts/metronic.js" type="text/javascript"></script>
    <script src="/Metronic/admin/layout/scripts/layout.js" type="text/javascript"></script>
    <!-- END PAGE LEVEL SCRIPTS -->


    <!-- END JAVASCRIPTS -->


    <script>
        jQuery(document).ready(function () {
            Metronic.init(); // init metronic core components
            Layout.init(); // init current layout
            Centro.init();
        });
    </script>
</body>
<!-- END BODY -->
</html>
codice:
var Centro = function () {
    
    var submitted = true;
    var handleCentro = function () {


        $('.form-data').validate({
            errorElement: 'span', //default input error message container
            errorClass: 'help-block help-block-error ', // default input error message class
            focusInvalid: false, // do not focus the last invalid input
            ignore: "",
            rules: {
            },


            messages: {
            },


            showErrors: function (errorMap, errorList) {
                if (submitted) {
                    var summary = "";
                    $.each(errorList, function () { summary += " * " + this.message + "<br />"; });
                    $('#dvError', $('.form-data')).find('span').html(summary);
                    submitted = false;
                }
                
                this.defaultShowErrors();
            },


            invalidHandler: function (event, validator) { //display error alert on form submit   
                $('#dvError', $('.form-data')).show();
                submitted = true;
            },


            highlight: function (element) { // hightlight error inputs
                $(element)
                    .closest('.form-group').addClass('has-error'); // set error class to the control group
            },


            success: function (label) {
                label.closest('.form-group').removeClass('has-error');
                label.remove();
            },


            errorPlacement: function (error, element) {
                //error.insertAfter(element);
                //error.insertAfter(element.closest('.input-group'))
            },


            submitHandler: function (form) {
                form.submit();
            }
        });
       
        $('.denominazione').rules('add', {
            required: true,
            messages: {
                required: 'Denominazione campo obbligatorio'
            }
        });


        $('[id$="btnSalva"]').click(function () {
            Metronic.blockUI({ boxed: true });


            $('#dvError', $('.form-data')).find('span').html('');
            $('#dvError', $('.form-data')).hide();


            var result = $('.form-data').valid();
            result &= checkDati();


            if (result == 0)
                Metronic.unblockUI();            


            return (result == 0 ? false : true);
        })        


        function checkDati() {
            var errore = false;
            var msgError = '';


            if (errore) {
                $('#dvError', $('.form-data')).show();
                $('#dvError', $('.form-data')).find('span').append(msgError);
            }            


            return !errore;
        }
    }


    return {
        //main function to initiate the module
        init: function () {           
            handleCentro();
        }


    };


}();
Quando clicco su 'Salva' ricevo un errore del tipo: 'oggetto non riconosciuto: span.help-block.help-block-error
Ho controllato il codice di esempio e sembra uguale. Non capisco dove sbaglio.
Prima utilizzavo un'altra versione di Metronic e non avevo nessun problema.
Grazie mille