SOLVED: WCF returns: "The remote server returned an error: NotFound."

[HWijngaarD]

As long as I return a windows known type the service works fine:
For example:

[ServiceContract]
	public interface ICalendarService
	{
		[OperationContract(AsyncPattern = true)]
		IAsyncResult BeginCreateCalenderItem(string applicationName, string subject, string body, string username, string password, AsyncCallback callBack, Object state);
		bool EndCreateCalenderItem(IAsyncResult result);
	}

But if I return my own type:

[ServiceContract]
	public interface IPhotoService
	{
		[OperationContract(AsyncPattern = true)]
		IAsyncResult BeginGetImagesFromAlbumByKeyWord(string keyString, string username, string password, AsyncCallback callBack, Object state);
		PhotoAlbum EndGetImagesFromAlbumByKeyWord(IAsyncResult result);
	}

With:

[DataContract]
	public class PhotoAlbum
	{
		[DataMember]
		public string Name { get; set; }

		[DataMember]
		public List<PhotoImage> Images { get; set; }
	}

And:

[DataContract]
	public class PhotoImage
	{
		[DataMember]
		public string URL { get; set; }

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

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

This returns the Error.
Has it something to do with system known types?