In my previous post , I mentioned that my biggest gripe with deriving from DependencyObject is that it is not serializable! I stand corrected (Well, almost). This is the code I tried initially BinaryFormatter serializer = new BinaryFormatter (); serializer.Serialize(stream, Assesments); And here is my exception Type 'MyHealth.Model.AssesmentCollection' in Assembly 'MyHealth, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable. To solve this problem...