iScrapbook uses a Core Data database to store the items you add to the Favorites bin. The Core Data database is a Mac OS X database solution. Under Mac OS X 10.4 (Tiger) a Core Data database has a size limit of 4GB's. Once this size limit is reached the error message "An error occurred while saving." will appear when you try to add another item to the Favorites bin. Under Mac OS X 10.5 (Leopard) this size limitation is no longer there.