Token StartElement in state Epilog would result in an invalid XML document with Soap Serializer

Hi, I need to serialize class into soap xml stream.

When I do xmlSerializer.Serialize I could see following error "Token StartElement in state Epilog would result in an invalid XML document with Soap Serializer"

Here Is just a few simple code in order to reproduce this behaviour.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Serialization;

namespace ConsoleApp1
{
    [SoapType(TypeName = "Child")]
    public class Child
    {
        public String ChildTag1 { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Serialization;

namespace ConsoleApp1
{
    [SoapType(TypeName = "Master"), SoapInclude(typeof(Child))]
    public class Master
    {
        public String MasterTag1 { get; set; }
        public Child[] Childs { get; set; }
    }
}

and finally xml soap serialization:

using System.IO;
namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Master mas = new Master();
            mas.MasterTag1 = "Tag1";
            Child ch1 = new Child();
            ch1.ChildTag1 = "Child1Tag1";
            Child ch2 = new Child();
            ch2.ChildTag1 = "Child2Tag1";
            mas.Childs = new Child[] { ch1, ch2 };

            MemoryStream target = new MemoryStream();
            System.Xml.Serialization.XmlTypeMapping xmlTypeMapping = (new System.Xml.Serialization.SoapReflectionImporter().ImportTypeMapping(mas.GetType()));
            System.Xml.Serialization.XmlSerializer xmlSerializer = new System.Xml.Serialization.XmlSerializer(xmlTypeMapping);
            xmlSerializer.Serialize(target, mas);
            byte[] result = target.ToArray();
        }
    }
}

When I comment out this line:  publicChild[]Childs{get;set;} on master.cs class all works fine!

Could anyone help me to solve this issue?

Thanks

FabioBo