asp.net mvc 4 - DataAnnotation for Required property

Question

First it works, but today it failed!

This is how I define the date property:

[Display(Name = "Date")]
[Required(ErrorMessage = "Date of Submission is required.")]        
[DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)]
[DataType(DataType.Date)]
public DateTime TripDate { get; set; }

It has been working in the past. But today, when I call the same ApiController action:

[HttpPost]
public HttpResponseMessage SaveNewReport(TripLeaderReportInputModel model)

The Firebug reports:

ExceptionMessage:

"Property 'TripDate' on type 'Whitewater.ViewModels.Report.TripLeaderReportInputModel' 
is invalid. Value-typed properties marked as [Required] must also be marked with
[DataMember(IsRequired=true)] to be recognized as required. Consider attributing the 
declaring type with [DataContract] and the property with [DataMember(IsRequired=true)]."

ExceptionType

"System.InvalidOperationException"

What happened? Isn't those [DataContract] for WCF? I am using the REST WebAPI in MVC4!

Can anyone help? please?

---update---

There are some similar links I have found.

MvC 4.0 RTM broke us and we don't know how to fix it RSS

--- update again ---

Here is the HTTP Response Header:

Cache-Control   no-cache
Connection  Close
Content-Length  1846
Content-Type    application/json; charset=utf-8
Date            Thu, 06 Sep 2012 17:48:15 GMT
Expires         -1
Pragma          no-cache
Server          ASP.NET Development Server/10.0.0.0
X-AspNet-Version    4.0.30319

Request Header:

Accept          */*
Accept-Encoding gzip, deflate
Accept-Language en-us,en;q=0.5
Cache-Control   no-cache
Connection          keep-alive
Content-Length  380
Content-Type    application/x-www-form-urlencoded; charset=UTF-8
Cookie          .ASPXAUTH=1FF35BD017B199BE629A2408B2A3DFCD4625F9E75D0C58BBD0D128D18FFDB8DA3CDCB484C80176A74C79BB001A20201C6FB9B566FEE09B1CF1D8EA128A67FCA6ABCE53BB7D80B634A407F9CE2BE436BDE3DCDC2C3E33AAA2B4670A0F04DAD13A57A7ABF600FA80C417B67C53BE3F4D0EACE5EB125BD832037E392D4ED4242CF6
DNT                 1
Host            localhost:39019
Pragma          no-cache
Referer         http://localhost:39019/Report/TripLeader
User-Agent          Mozilla/5.0 (Windows NT 6.1; WOW64; rv:15.0) Gecko/20100101 Firefox/15.0
X-Requested-With    XMLHttpRequest

--- update ---

I have found out a makeshift solution. See answer below. If anyone understand why it works or has better solutions, please post your answers. Thank you.

Answer 1

Okay. Though I have not complete understood this thing. A workaround is found.

In Global.asax:

GlobalConfiguration.Configuration.Services.RemoveAll(
    typeof(System.Web.Http.Validation.ModelValidatorProvider),
    v => v is InvalidModelValidatorProvider);

I found it in the Issue Tracker in aspnetwebstack. Here is the link to the page:

Overly aggressive validation for applying [DataMember(IsRequired=true)] to required properties with value types

If anyone can tell us why it is like this, please post your insight as answers. Thank you.