不能序列化System.ComponentModel.ISite类型的成员

我正在尝试运行向量。在web浏览器中打开Asmx并得到以下错误。有什么问题吗?

不能序列化System.ComponentModel.MarshalByValueComponent.Site类型为System.ComponentModel.ISite的成员，因为它是一个接口。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
namespace WebApplication2
{
    /// <summary>
    /// Summary description for Vector
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    public class Vector : System.Web.Services.WebService
    {
        public double X { get; set; }
        public double Y { get; set; }
        public double Z { get; set; }


        [WebMethod]
        public double MagnitudeSquared()
        {
            return X * X + Y * Y + Z * Z;
        }

        [WebMethod]
        public double Magnitude()
        {
            return Math.Sqrt(MagnitudeSquared());
        }
        [WebMethod]
        public static Vector operator -(Vector v1, Vector v2)
        {
            Vector result = new Vector();
            result.X = v1.X - v2.X;
            result.Y = v1.Y - v2.Y;
            result.Z = v1.Z - v2.Z;
            return result;
        }
        [WebMethod]
        public static Vector operator +(Vector v1, Vector v2)
        {
            Vector result = new Vector();
            result.X = v1.X + v2.X;
            result.Y = v1.Y + v2.Y;
            result.Z = v1.Z + v2.Z;
            return result;
        }

        [WebMethod]
        public static Vector operator *(Vector v1, double factor)
        {
            Vector result = new Vector();
            result.X = v1.X * factor;
            result.Y = v1.Y * factor;
            result.Z = v1.Z * factor;
            return result;
        }
        [WebMethod]
        public Vector Clone()
        {
            Vector result = new Vector();
            result.X = this.X;
            result.Y = this.Y;
            result.Z = this.Z;
            return result;
        }
    }
}