I found that the materialized object did not have a reference to the Bloc space. With the line of code introduced below the error disappeared. | container materializedObject objectToSerlialize | container := BlMorph new withRectangleViewDo: [ :v | v extent: 200@200. v color: Color lightCyan ]. objectToSerlialize := BlMorph new withRectangleViewDo: [ :v | v extent: 20@20. v color: Color blue]. container openInWorld. container addMorphCentered: objectToSerlialize. self confirm: 'Save?'. FLSerializer serialize: objectToSerlialize toFileNamed: 'demo.fuel'. self confirm: 'Delete?'. objectToSerlialize delete. self confirm: 'Restore?'. materializedObject := FLMaterializer materializeFromFileNamed: 'demo.fuel'. "Restoring Bloc space" materializedObject space: container space. container addMorph: materializedObject ----- http://chicoary@gmail.com -- View this message in context: http://forum.world.st/Fuel-and-Bloc-error-on-materializing-tp4862550p4862577... Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.