[DataContract]
 public class Response
 {
     [DataMember]
     public object Result { get; set; }

     [DataMember]
     public string Erorr { get; set; }
 }



  public Response GetData()
  {
     return new Response { Result = new MemoryStream()};
  }

  public Stream Test()
  {
     return new MemoryStream();
  }