Serialization Problem in Singleton class

FileStream fs = new FileStream("DataFile.dat", FileMode.Create);
try
{
    // Construct a BinaryFormatter and use it  //to serialize the data to the stream.
     BinaryFormatter formatter = new BinaryFormatter();                
     formatter.Serialize(fs, Obj);
}
catch (SerializationException e)
{
    Console.WriteLine("Failed to serialize. Reason: " + e.Message);
    throw;
}
finally
{
    fs.Close();
}

using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;


namespace Namespace
{
    [Serializable]

public sealed class Singleton: ISerializable
    {
        private static readonly Singleton Obj = new Singleton ();

        private Singleton() { }

        public static Singleton GetInstance
        {
            get
            {                
                return Obj;
            }
        }

        internal sealed class SingletonSerializationHelper : IObjectReference
        {
            // This object has no fields (although it could).

            // GetRealObject is called after this object is deserialized.
            public Object GetRealObject(StreamingContext context)
            {
                // When deserialiing this object, return a reference to
                // the Singleton object instead.
                return Singleton.Obj;
            }
        }
        public void GetObjectData(SerializationInfo info, StreamingContext context)
        {

            info.SetType(typeof(SingletonSerializationHelper));
        }