I recently ran into an odd and annoying error when working with the DataContractSerializer class for a WP7 project. I thought I’d share it to save others who might encounter it the same annoyance I had. So I had an instance of ObservableCollection<T> that I was trying to serialize (with T being a class I wrote for the project) and whenever it would hit the code to save it, it would give me: The data contract type 'ProjectName.MyMagicItemsCl... is not serializable because it is not public. ......