ASP.net下拉列表未将所选值保存到数据库

在下面的代码中,我想将用户从dropdownlist选择的值保存到数据库中。但无论用户选择什么值,下拉式lsit的第一个值都会保存到数据库中

视图

<% =Html.DropDownList("lstUsertype", (SelectList)ViewData["UserTypeID"])%>

public ActionResult CreateUser()
        {
            UmUser _UmUser = new UmUser();
            UMRepository _UMRepository = new UMRepository();
            EvoLetDataContext db = new EvoLetDataContext();
            ViewData["UserTypeID"] = new SelectList(_UMRepository.FillUserTypes(), "UserTypeID", "UserType",2);
            return View(_UmUser);
    }

    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult CreateUser(UmUser _umUser)
    {
        //try
        //{
            if (ModelState.IsValid)
            {

                //try
                //{
                    UserRepository _UserRepository = new UserRepository();

                    _UserRepository.Add(_umUser);
                    _UserRepository.Save();
                    return RedirectToAction("Details", new { id = _umUser.UserID });
                /*}
                catch
                {
                    ModelState.AddModelErrors(_umUser.GetRuleViolations());
                }*/
            }

            return View();
        //}
        /*catch
        {
            return View();
        }*/
    }