I'm creating a mvc login form for existing Umbraco site I'm using Html.BeginUmbracoForm on the View, SurfaceController is called, but it fires "Can only use UmbracoPageResult in the context of an Http POST when using a SurfaceController form" exception

My SurfaceController:
 [HttpGet]
        [ActionName("MemberLogin")]
        public ActionResult MemberLoginGet()
        {
            return View("MemberLogin", new MemberLoginModel());
        }

        // The MemberLogout Action signs out the user and redirects to the site home page:

    [HttpGet]
    public ActionResult MemberLogout()
    {
        Session.Clear();
        FormsAuthentication.SignOut();
        return Redirect("/");
    }

    [HttpPost]
    [ActionName("MemberLoginPost")]
    public ActionResult MemberLoginPost(MemberLoginModel model)
    {
        if (ModelState.IsValid && !MembersManager.IsMemberSponsor(model.Username))
        {
            result = MembersManager.AuthenticateUser(model.Username, model.Password);
            if (result.IsAuthenticated)
            {
                model.Username = MembersManager.GetActualLoginString(model.Username);
                FormsAuthentication.SetAuthCookie(model.Username, model.RememberMe);
                return RedirectToUmbracoPage(32684);
            }
            else
            {
                return View("MemberLogin");
            }
        }
        else
        {
            return CurrentUmbracoPage();
        }
    }

And the View:

@if (!User.Identity.IsAuthenticated)
{
    using (Html.BeginUmbracoForm<Controllers.MemberLoginSurfaceController>("MemberLoginPost",  FormMethod.Post, new { action = this.Url.Action("MemberLoginPost","MemberLoginSurface") }))
    {
        <div id="wrapper">
            <div class="form-auth">
                <ul class="auth">
                    <li>
                        <label>
                            E-mail</label>
                        @Html.TextBoxFor(x => x.Username)
                        @Html.ValidationMessageFor(x => x.Username)
                    </li>
                    <li>
                        <label>
                            Пароль</label>
                        <span class="input-block">
                            @Html.PasswordFor(x => x.Password)
                            @Html.ValidationMessageFor(x => x.Password)
                    </li>
                </ul>
                <div class="remember">
                    @Html.CheckBoxFor(x => x.RememberMe)
                    <label>
                        Запомнить</label>
                </div>
                <div class="submit">
                    <input type="submit" runat="server" id="usLoginButton" value="Войти"/>
                </div>
            </div>
        </div>
    }
}

What should I do?