无法在C＃中反序列化JSON结果。输入字符串格式错误

我正在尝试将json输出反序列化为C＃对象。JSON结果：

{"order":{"commission":3.490000,"cost":4.490000,"duration":"day","extended_hours
":false,"fees":0.000000,"class":"equity","price":1.000000,"quantity":1.000000,"r
equest_date":"2013-11-26T09:43:17.118Z","result":true,"side":"buy","status":"ok"
,"symbol":"DIS","type":"limit"}}

我从JSON派生的类：

    public class Rootobject
{
    public Order Order { get; set; }
}

public class Order
{
    public float commission { get; set; }
    public float cost { get; set; }
    public string duration { get; set; }
    public bool extended_hours { get; set; }
    public int fees { get; set; }
    public string _class { get; set; }
    public int price { get; set; }
    public int quantity { get; set; }
    public DateTime request_date { get; set; }
    public bool result { get; set; }
    public string side { get; set; }
    public string status { get; set; }
    public string symbol { get; set; }
    public string type { get; set; }
}

用于反序列化的代码（来自Newtonsoft的JSON.NET）：

 Rootobject ord = JsonConvert.DeserializeObject<Rootobject>(responsebody);

我收到以下错误。

 Unhandled Exception: System.FormatException: Input string was not in a correct format.
   at Newtonsoft.Json.Utilities.ConvertUtils.Int32Parse(Char[] chars, Int32 start, Int32 length)
   at Newtonsoft.Json.JsonTextReader.ParseNumber()
   at Newtonsoft.Json.JsonTextReader.ParseValue()
   at Newtonsoft.Json.JsonTextReader.ReadInternal()
   at Newtonsoft.Json.JsonReader.ReadAsInt32Internal()
   at Newtonsoft.Json.JsonTextReader.ReadAsInt32()
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.ReadForType(Jso
nReader reader, JsonContract contract, Boolean hasConverter)

我试过将反序列化的结果保存到工作正常的“动态”对象中。但是我不想使用动态对象来映射字段。

请指教。

注意：第三方API也会发送一个名为“ class”的字段。当我尝试直接调用该字段时遇到编译时错误，我该如何称呼它。