Apparently I’m not the only one to have this sneaky little problem that has been driving me mad. Given the simple model:

public class Foo {
    [Required] public string Bar {get;set;}
}

And a simple view:

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master"
Inherits="System.Web.Mvc.ViewPage<Foo>" %>
<%@ Import Namespace="MvcApplication2.Models"%>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
	Index
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">

<script src="/Scripts/jquery-1.3.2.js" type="text/javascript"></script>
<script src="/Scripts/jquery.validate.js" type="text/javascript"></script>
<script src="/Scripts/MicrosoftMvcJQueryValidation.js" type="text/javascript"></script>

 <h2>Index</h2>
 <%= Html.ValidationSummary() %>
 <% Html.EnableClientValidation(); %>
 <%
  using (Html.BeginForm())
  {
    ViewContext.FormContext.ClientValidationFunction = "EnableClientValidation"; %>
    <%= Html.LabelFor(x=>x.Bar) %>
    <%= Html.TextBoxFor(x=>x.Bar) %>
    <input type="submit" />
<%  } %>
</asp:Content>

You would expect the form to emit the JSON needed to pass to the jQuery validator right? WRONG! It just outputs the following

<script type="text/javascript">
//<![CDATA[
EnableClientValidation({"Fields":[],"FormId":"form0"}, null);
//]]>
</script>

That’s no help; however, when you give it the <%= Html.ValidationMessageFor(x=>x.Bar) %> you start to see what you expect.