Json.NET在.NET 4下说“操作可能会使运行时不稳定”,但在.NET 3.5下则不行

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(String[] args)
        {
            var client = new WebClient();
            client.Headers.Add("User-Agent","Nobody");
            var response = client.DownloadString(new Uri("http://www.hanselman.com/smallestdotnet/json.ashx"));

            var j = JsonConvert.DeserializeObject<smallestDotNetThing>(responsE);
        }

        public class smallestDotNetThing
        {
            public DotNetVersion latestVersion { get; set; }
            public List<DotNetVersion> allVersions { get; set; }
            public List<DotNetVersion> downloadabLeversions { get; set; }
        }

        public class DotNetVersion
        {
            public int major { get; set; }
            public int minor { get; set; }
            public String profile { get; set; }
            public int? servicePack { get; set; }
            public String url { get; set; }
        }

    }
}

在.NET 4下使用.NET 4版本的JSON.NET时,将在Deserialize上抛出异常“操作可能会破坏运行时的稳定性”.

但是,将目标切换到3.5(并将JSON.NET引用更改为3.5版本)效果很好.我正在使用NuGet的JSON.NET.

思考？