Hi Damien, The method NSAbstractDataStream class >>initialize contains the following code: -=-=-=-=-=-=-=-=-= Smalltalk do: [:cls | cls isInMemory ifTrue: [ cls isBehavior ifTrue: [ cls isPointers not & cls isVariable & cls isWords ifTrue: [ (t includesKey: cls) ifFalse: [t at: cls put: 20]]]]]. -=-=-=-=-=-=-=-=-= The problem is that isInMemory is not in Pharo 1.1 anymore. I think that you can remove the condition "cls isInMemory ifTrue: [". Maybe someone else can confirm? Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;. -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.