为什么判断不了会员等级？？？

我的users表里面是每人的信息，我在登陆的时候判断是普通会员还是管理员，下面是管理员专用登陆框，为什么判断不了呢？
public partial class Admin_gd_login : System.Web.UI.Page
{
    User user = new User();
    protected void Page_Load(object sender, EventArgs e)
    {
        
    }
    protected void btnAdminLogin_Click(object sender, EventArgs e)
    {
        if (this.txtAdminName.Text == "" || this.txtAdminPsw.Text == "")
        {
            this.Page.ClientScript.RegisterStartupScript(this.GetType(), "", "<script>alert('用户名或密码不能为空！')</script>");
        }
        if (UserManager.GetUserByLoginId(this.txtAdminName.Text) != null)
        {
            user = UserManager.GetUserByLoginId(this.txtAdminName.Text);            if (user.MemberGrade.ToString()=="管理员")
            {
                if (UserManager.ManagerLogin(this.txtAdminName.Text, this.txtAdminPsw.Text, out user))
                {
                    Session["AdminName"] = this.txtAdminName.Text;
                    Response.Redirect("gd_admin.aspx");
                }
                else
                {
                    this.Page.ClientScript.RegisterStartupScript(this.GetType(), "", "<script>alert('用户名或密码错误！')</script>");
                    return;
                }
            }
            else
            {
                this.Page.ClientScript.RegisterStartupScript(this.GetType(), "", "<script>alert('对不起，您不是管理员！')</script>");
                return;
            }
        }
    }
    protected void btnAdminCancel_Click(object sender, EventArgs e)
    {
        Response.Redirect("~/index.aspx");
    }
}