[XmlRpcUrl("https://blabala.com/rpc")] // описание методов
public interface Trac : IXmlRpcProxy
{
    [XmlRpcMethod("ticket.get")]  //
    object[] get(int id);

    [XmlRpcMethod("ticket.getActions")]  //
    object[] getActions(int id);
}

public partial class DHL : Form
{
    public DHL()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        int id = 6;
        get(id);
    }

    private void get(int id)
    {
        Trac proxy;
        string user = "uzer";
        string password = "parol";
        proxy = XmlRpcProxyGen.Create<Trac>();
        proxy.Credentials = new System.Net.NetworkCredential(user, password);
         object[] arr = proxy.get(id);
         BinaryFormatter formatter = new BinaryFormatter();
        using (FileStream fs = new FileStream("arr.dat", FileMode.OpenOrCreate))
          {
              formatter.Serialize(fs, arr);// тут и ошибка, что Тип CookComputing.XmlRpc.XmlRpcStruct в сборке CookComputing.XmlRpcV2, Version=3.0.0.0, Culture=neutral, PublicKeyToken=a7d6e17aa302004d не отмечен как сериализуемый.
          }
    }

    private void button4_Click(object sender, EventArgs e)
    {
        int id = 6;
        getActions( id);
    }

    private void getActions(int id)
    {
        Trac proxy;
        string user = "uzer";
        string password = "parol";
        proxy = XmlRpcProxyGen.Create<Trac>();
        proxy.Credentials = new System.Net.NetworkCredential(user, password);
        object[]  arr = proxy.getActions(id);
        BinaryFormatter formatter = new BinaryFormatter();
        using (FileStream fs = new FileStream("arr.dat", FileMode.OpenOrCreate))
        {
        formatter.Serialize(fs, arr);//а тут нет такой ошибки
        }
    }
}

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public DriversLicense License;
}


// An instance of this type will be part of the object graph and will need to be
// serialized also.
public class DriversLicense
{
    public string Number { get; set; }
}

public class PersonSurrogate : ISerializationSurrogate
{
    /// <summary>
    /// Manually add objects to the <see cref="SerializationInfo"/> store.
    /// </summary>
    public void GetObjectData(object obj, SerializationInfo info, StreamingContext context)
    {
        Person person = (Person) obj;
        info.AddValue("Name", person.Name);
        info.AddValue("Age", person.Age);
        info.AddValue("License", person.License);
    }

    /// <summary>
    /// Retrieves objects from the <see cref="SerializationInfo"/> store.
    /// </summary>
    /// <returns></returns>
    public object SetObjectData(object obj, SerializationInfo info, StreamingContext context, ISurrogateSelector selector)
    {
        Person person = (Person)obj;
        person.Name = info.GetString("Name");
        person.Age = info.GetInt32("Age");
        person.License = (DriversLicense) info.GetValue("License", typeof(DriversLicense));
        return person;
    }
}

public class DriversLicenseSurrogate : ISerializationSurrogate
{
    /// <summary>
    /// Manually add objects to the <see cref="SerializationInfo"/> store.
    /// </summary>
    public void GetObjectData(object obj, SerializationInfo info, StreamingContext context)
    {
        DriversLicense license = (DriversLicense)obj;
        info.AddValue("Number", license.Number);
    }

    /// <summary>
    /// Retrieves objects from the <see cref="SerializationInfo"/> store.
    /// </summary>
    /// <returns></returns>
    public object SetObjectData(object obj, SerializationInfo info, StreamingContext context, ISurrogateSelector selector)
    {
        DriversLicense license = (DriversLicense)obj;
        license.Number = info.GetString("Number");
        return license;
    }
}

private static void SerializePerson(Person person)
{
    if (person == null)
        throw new ArgumentNullException("person");

    using (var memoryStream = new MemoryStream())
    {
        //Configure our surrogate selectors.
        var surrogateSelector = new SurrogateSelector();
        surrogateSelector.AddSurrogate(typeof (Person), new StreamingContext(StreamingContextStates.All),
                                       new PersonSurrogate());
        surrogateSelector.AddSurrogate(typeof (DriversLicense), new StreamingContext(StreamingContextStates.All),
                                       new DriversLicenseSurrogate());

        //Serialize the object
        IFormatter formatter = new BinaryFormatter();
        formatter.SurrogateSelector = surrogateSelector;
        formatter.Serialize(memoryStream, person);

        //Return to the beginning of the stream
        memoryStream.Seek(0, SeekOrigin.Begin);

        //Deserialize the object
        Person deserializedPerson = (Person) formatter.Deserialize(memoryStream);
    }
}