Hi guys I'm trying to load VW2.5.2 (yes nearly 20 years old code in Pharo and I will introduce a real exception instead of this bad and generic error. What do you think? importFor: requestor (self existsBehavior) ifFalse: [ self error: ('Cannot install method in unexistent behavior {1}' format: { behaviorName asString } ) ]. requestor ifNotNil: [ requestor contents ifNil: [ requestor contents: contents ]]. ^self targetClass compile: contents classified: categoryName withStamp: stamp notifying: requestor Stef