public class Catalog
{
    public int id { get; set; }
    public int pid { get; set; }
    public string title { get; set; }

}

public ViewResult Create()
    {

        List<SelectListItem> list = new List<SelectListItem>();
        list.Add(new SelectListItem() { Value = "0", Text = "Без родителя" });
        foreach (var p in repository.Catalogs)
        {
            list.Add(new SelectListItem() { Value = p.id.ToString(), Text = p.title });
        }
        ViewBag.DropDownValues = new SelectList(list, "Value", "Text");
        ViewBag.FormTitle = null;
        return View();
    }
    [HttpPost]
    public ActionResult Create(Catalog catalog)
    {
        if (ModelState.IsValid)
        {
            repository.SaveCatalog(catalog);
            TempData["message"] = string.Format("Новая категория "{0}" была сохранены", catalog.title);
            return RedirectToAction("Index");
        }
        else
        {
            return View(catalog);
        }
    }

public void SaveCatalog(Catalog catalog)
    {
        if (catalog.id == 0)
            context.Catalogs.Add(catalog);
        else
        {
            Catalog dbEntry = context.Catalogs.Find(catalog.id);
            if (dbEntry != null)
            {
                dbEntry.pid = catalog.pid;
                dbEntry.title = catalog.title;
            }
        }
        context.SaveChanges();
    }

@model EStore.Domain.Entities.Catalog

@{
    ViewBag.TitlePage = "Админ панель: добавление категории";
    Layout = "~/Views/Shared/_AdminLayout.cshtml";
}

<div class="panel">
    <div class="panel-heading">
        <h3>Создание категории</h3>
    </div>

    @using (Html.BeginForm("Create", "Addcatalog"))
    {
        <div class="panel-body">
            <div class="form-group">
                @Html.HiddenFor(m => m.id)
                @Html.Label("Родительская категория: ", new { @class = "col-md-2 control-label" })
                @Html.DropDownList("pid", ViewBag.DropDownValues as SelectList, new { @class = "form-control" })
                @Html.Label("Название категории: ", new { @class = "col-md-2 control-label" })
                @Html.TextBox("title", null, new { @class = "form-control" })
            </div>

        </div>
        <div class="panel-footer">
            <input type="submit" value="Сохранить" class="btn btn-primary" />
            @Html.ActionLink("вернуться к списку", "Index", null, new
            {
                @class = "btn btn-default"
            })
        </div>
    }
</div>

The ViewData item that has the key 'pid' is of type 'System.Int32' but must be of type 'IEnumerable<SelectListItem>'.