我是这样写的
private void buttonEnter_Click(object sender, EventArgs e)
        {
            int t = 1;
            SqlConnection ConnectionLogin = new SqlConnection(@"Server=(local)\sqlexpress;Integrated Security=True;Database=Mydata");
            ConnectionLogin.Open();
            SqlCommand CommandLogin = ConnectionLogin.CreateCommand();
             = "SELECT ID,Password,BuyIn,SellOut,Stat,Register,Append,Printer form IDData";
            SqlDataReader ReadLogin = CommandLogin.ExecuteReader();
            while (ReadLogin.Read())
            {
                if (ReadLogin.GetValue(0).ToString() == textBoxID.Text &&
ReadLogin.GetValue(0).ToString() == textBoxPassword.Text)
                {
                    break;
                    if (ReadLogin.GetInt32(3) >= t)
                    {
                        MDI.VToolStripMenuItemBuyIn.Visible = false; //这个提示错误
                    }
                    MDI mdi=new MDI();
                    mdi.Show();
                }
            }
                    
        }
错误内容：
非静态的字段、方法或属性“MyTestData.MDI.VToolStripMenuItemBuyIn”要求对象引用    E:\My Documents\Visual Studio 2005\Projects\MyTestData\MyTestData\Login.cs    35    25    MyTestData

请问这个该如何操作这个MDI窗口中的菜单显示是否啊？