In the EnterprisePharo Book there is a chapter "Fuel Format Migration". There the format migration form Fuel version 1.7 to 1.9 is shown. I ask me if there is a similar possibility for the migration between Fuel in Pharo 4 and 6. Johannes Am 05.08.2017 um 15:08 schrieb Cyril Ferlicot <cyril.ferlicot@gmail.com<mailto:cyril.ferlicot@gmail.com>>: On sam. 5 août 2017 at 13:10, Johannes Brauer <brauer@nordakademie.de<mailto:brauer@nordakademie.de>> wrote: Peter Your suggestion is correct. I correct the expression to (FLMaterializer materializeFromFileNamed: aFileRefence fullName) Now I get another exception. KeyNotFound: key #'ositive8SmallIntegerClusterJ 4à 1â ð+ â( %? "< 9 ª 6P M ¾0 d *ÃD ''x ! Å 8' not found in SystemDictionary I think this is a compatibility problem between different Fuel versions. Hi, If you use Fuel to serialize objects with Pharo 4, then you can only materialize them with a Fuel from Pharo 4. Other versions of Fuel will not be able to read them. Johannes -- Cyril Ferlicot https://ferlicot.fr http://www.synectique.eu 2 rue Jacques Prévert 01, 59650 Villeneuve d'ascq France