在windows mobile 使用Newtonsoft.Json 报错？

[葫芦娃的博客]

 Product product = new Product()
            {
                Name = "android",
                Expiry = DateTime.Now,
                Price = 2000,
                Sizes = new string[] { "1.5", "2.2", "4.1" }
            };
            var json = JsonConvert.SerializeObject(product);
            MessageBox.Show(json);