Eu pesquisei sobre esse problema no Google e verifiquei meu web.config, bundleconfig e meu layout com a seguinte aparência: web.config:

<appSettings>
    <add key="webpages:Version" value="3.0.0.0" />
    <add key="webpages:Enabled" value="false" />
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />
</appSettings>

Na minha pasta App_Start em "BundleConfig.cs":

        var jqueryBundle = new ScriptBundle("~/bundles/jquery");
        jqueryBundle.Include("~/Scripts/jquery-{version}.js");
        jqueryBundle.Include("~/Scripts/moment.min.js");
        jqueryBundle.Include("~/Scripts/loadingoverlay.js");
        jqueryBundle.Include("~/Scripts/fullcalendar.js");
        jqueryBundle.Include("~/Scripts/lang-all.js");
        jqueryBundle.Transforms.Add(jsTransformer);
        jqueryBundle.Orderer = nullOrderer;
        bundles.Add(jqueryBundle);

var jqueryvalBundle = new ScriptBundle ("~ / bundles / jqueryval"); jqueryvalBundle.Include ("~ / Scripts / jquery.validate *"); jqueryvalBundle.Include ("~ / Scripts / jquery.validate.js"); jqueryvalBundle.Include ("~ / Scripts / jquery.validate.unobtrusive.js"); jqueryvalBundle.Transforms.Add (jsTransformer); jqueryvalBundle.Orderer = nullOrderer; bundles.Add (jqueryvalBundle);

na minha página de layout:

@Scripts.Render("~/bundles/jquery")
@Scripts.Render("~/bundles/jqueryval")
@Scripts.Render("~/bundles/bootstrap")

Firebug mostra:

Até agora, tudo está incluído e deve estar funcionando sem problemas.

Meu modelo:

   [DisplayName("Förnamn")]
    [Required(ErrorMessage = "Vänligen ange ett förnamn")]
    [StringLength(100)]
    public string FirstName { get; set; }
    [DisplayName("Efternamn")]
    [Required(ErrorMessage = "Vänligen ange ett efternamn")]
    [StringLength(100)]
    public string LastName { get; set; }
    [DisplayName("E-post")]
    [Required(ErrorMessage = "Vänligen ange epost")]
    [StringLength(100)]
    [EmailAddress(ErrorMessage = "Ange en korrekt e-postaddress")]
    public string Email { get; set; }
    [DisplayName("Mobil")]
    [DataType(DataType.PhoneNumber)]
    public string PhoenNumber { get; set; }
    [DataType(DataType.Password)]
    [DisplayName("Lösenord")]
    public string PassWord { get; set; }

Minha visão:

<div class="col-md-4 col-xs-12">
        @using (Html.BeginForm(null, null, FormMethod.Post, new { id = "credentialsForm" }))
        {
            @Html.AntiForgeryToken()

            <div class="form-horizontal">
                @Html.ValidationSummary(true, "", new { @class = "text-danger" })
                <div class="form-group createCustomerFormGroup">
                    @Html.LabelFor(model => model.FirstName, htmlAttributes: new { @class = "control-label col-md-3" })
                    <div class="col-md-9">
                        @Html.EditorFor(model => model.FirstName, new { htmlAttributes = new { @class = "form-control", @name = "FirstName" } })
                        @Html.ValidationMessageFor(model => model.FirstName, "", new { @class = "text-danger" })
                    </div>
                </div>

                <div class="form-group createCustomerFormGroup">
                    @Html.LabelFor(model => model.LastName, htmlAttributes: new { @class = "control-label col-md-3" })
                    <div class="col-md-9">
                        @Html.EditorFor(model => model.LastName, new { htmlAttributes = new { @class = "form-control" } })
                        @Html.ValidationMessageFor(model => model.LastName, "", new { @class = "text-danger" })
                    </div>
                </div>

                <div class="form-group createCustomerFormGroup">
                    @Html.LabelFor(model => model.Email, htmlAttributes: new { @class = "control-label col-md-3" })
                    <div class="col-md-9">
                        @Html.EditorFor(model => model.Email, new { htmlAttributes = new { @class = "form-control" } })
                        @Html.ValidationMessageFor(model => model.Email, "", new { @class = "text-danger" })
                    </div>
                </div>

                <div class="form-group createCustomerFormGroup">
                    @Html.LabelFor(model => model.PassWord, htmlAttributes: new { @class = "control-label col-md-3" })
                    <div class="col-md-9">
                        @Html.EditorFor(model => model.PassWord, new { htmlAttributes = new { @class = "form-control" } })
                        @Html.ValidationMessageFor(model => model.PassWord, "", new { @class = "text-danger" })
                    </div>
                </div>

                <div class="form-group createCustomerFormGroup">
                    @Html.LabelFor(model => model.PhoenNumber, htmlAttributes: new { @class = "control-label col-md-3" })
                    <div class="col-md-9">
                        @Html.EditorFor(model => model.PhoenNumber, new { htmlAttributes = new { @class = "form-control" } })
                        @Html.ValidationMessageFor(model => model.PhoenNumber, "", new { @class = "text-danger" })
                    </div>
                </div>
            </div>
        }
</div>

um campo no formulário via firebug:

Eu executo esse script no firebug e não recebo erros, mesmo que deva haver erros, pois alguns dos campos são solicitados, mas eles não têm um valor:

$("#credentialsForm").validate().numberOfInvalids()
// retunrs 0

$("#credentialsForm").validate().valid()
// returns true

Eu estive nisso por horas e estou ficando louco agora, o que estou perdendo?

EDIT: mudou a pergunta de "Como configurar a validação discreta do MVC 5 corretamente" para o título atual, pois descreveu o que eu estava procurando melhor que o título anterior.