I'm trying to make a log-in log-off with Ajax supported.

I made some logic in my controller to sign the user in and then return simple partial containing welcome message and log-Off ActionLink my Action method looks like this :

public ActionResult LogOn(LogOnModel model, string returnUrl)
{
    if (ModelState.IsValid)
    {
        if (MembershipService.ValidateUser(model.UserName, model.Password))
        {
            FormsService.SignIn(model.UserName, model.RememberMe);
            if (Request.IsAjaxRequest())
            {
             //HERE IS THE PROBLEM :(
                return View("LogedInForm");
            }
            else
            {
                if (!String.IsNullOrEmpty(returnUrl))
                    return Redirect(returnUrl);
                else
                    return RedirectToAction("Index", "Home");
            }
        }
        else
        {
            ModelState.AddModelError("", "The user name or password provided is incorrect.");
            if (Request.IsAjaxRequest())
            {
                return Content("There were an error !");
            }
        }
    }
    return View(model);
}

and I'm trying to return this simple partial :

 Welcome <b><%= Html.Encode(Model.UserName)%></b>!
 <%= Html.ActionLink("Log Off", "LogOff", "Account") %>

and of-course the two partial are strongly-typed to LogOnModel.

But if i returned View("PartialName") i always get OnFailure with status code 500. While if i returned Content("My Message") everything is going right.

so please tell me why i always get this "StatusCode = 500" ??. where is the big mistake ??.

By the way in my Site MasterPage i rendered partial to show long-on simple form this partial looks like this :

<script type="text/javascript">
    function ShowErrorMessage(ajaxContext) {
        var response = ajaxContext.get_response();
        var statusCode = response.get_statusCode();
        alert("Sorry, the request failed with status code " + statusCode);
    }
    function ShowSuccessMessage() {
        alert("Hey everything is OK!");
    }
</script>

  <div id="logedInDiv">
  </div>

        <% using (Ajax.BeginForm("LogOn", "Account", new AjaxOptions
           {
               UpdateTargetId = "logedInDiv",
               InsertionMode = InsertionMode.Replace,
               OnSuccess = "ShowSuccessMessage",
               OnFailure = "ShowErrorMessage"
           }))
           { %>
            <%= Html.TextBoxFor(m => m.UserName)%>
            <%= Html.PasswordFor(m => m.Password)%>
            <%= Html.CheckBoxFor(m => m.RememberMe)%>

            <input type="submit" value="Log On" />
        < <% } %>