WCF、MVC4和身份验证:自定义错误

我正在尝试自定义Visal Studio项目提供的"默认身份验证"。我有一个数据库，里面有一些用户，链接到我的项目。我想做的是：确保登录名/密码对在数据库中，从而连接用户。

只是想告诉你已经做了什么：会计主管：

 [HttpPost]
 [AllowAnonymous]
 [ValidateAntiForgeryToken]
 public ActionResult Login(LoginModel model, string returnUrl)
 {
    try
    {
        var context = new MyService.MyEntities2(new Uri("http://localhost:12345/MyWS.svc/"));
        var usr = from user in context.PERSON
                  where user.LOGIN == model.UserName && user.PASSWORD == model.Password
                  select user;
        List<MyWebPortal.MyService.PERSON> lpers = usr.ToList();
        int nbRes = lpers.Count();
        if (ModelState.IsValid && nbRes ==1)
        {
            return RedirectToLocal(returnUrl);
        }
    }
    catch (DataServiceQueryException ex)
    {
        ModelState.AddModelError("", "Erreur : "+ex.ToString());
    }
    ModelState.AddModelError("", "Authentication error");
    return View(model);
}

登录型号：

public class LoginModel
    {
        [Required]
        [Display(Name = "User name")]
        public string UserName { get; set; }
        [Required]
        [DataType(DataType.Password)]
        [Display(Name = "Password")]
        public string Password { get; set; }
    }

登录形式：

@using (Html.BeginForm(new { ReturnUrl = ViewBag.ReturnUrl })) {
@Html.AntiForgeryToken()
@Html.ValidationSummary(true)
<fieldset>
    <ol>
        <li>
            @Html.LabelFor(m => m.UserName)
            @Html.TextBoxFor(m => m.UserName)
            @Html.ValidationMessageFor(m => m.UserName)
        </li>
        <li>
            @Html.LabelFor(m => m.Password)
            @Html.PasswordFor(m => m.Password)
            @Html.ValidationMessageFor(m => m.Password)
        </li>
    </ol>
    <input type="submit" value="Login" />

但我有以下错误：

System.Data.Services.Client.DataServiceQueryException: Une erreur s'est produite lors du traitement de cette requête. ---> System.Data.Services.Client.DataServiceClientException: <?xml version="1.0" encoding="utf-8" standalone="yes"?><error xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"><code></code><message xml:lang="fr-FR">Une erreur s'est produite lors du traitement de cette requête.</message></error> 
à System.Data.Services.Client.QueryResult.ExecuteQuery(DataServiceContext context) 
à System.Data.Services.Client.DataServiceRequest.Execute[TElement](DataServiceContext context, QueryComponents queryComponents) 
--- Fin de la trace de la pile d'exception interne --- 
à System.Data.Services.Client.DataServiceRequest.Execute[TElement](DataServiceContext context, QueryComponents queryComponents) 
à System.Data.Services.Client.DataServiceQuery`1.Execute() 
à System.Data.Services.Client.DataServiceQuery`1.GetEnumerator() 
à System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) 
à System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source) 
à MyApp.Controllers.AccountController.Login(LoginModel model, String returnUrl) dans d:'....'Documents'Visual Studio 2012'Projects'MyProg'MyWS'Controllers'AccountController.cs:ligne 45

其中ligne 45是

List<MyWebPortal.MyService.PERSON> lpers = usr.ToList();

我的请求有错吗？谢谢

var context = new SteelcaseService.SteelcaseEntities2(new Uri("http://localhost:12345/Steelcase.svc/"));
----> var persons = context.PERSON.ToList();
var usr = from user in persons
          where user.LOGIN == model.UserName && user.PASSWORD == model.Password
          select user;