Hi esteban I'm looking for a change due to the TreePackage introduction. Before I could simply do something like the following to unload Nautilus Smalltalk tools remove: #browser. Smalltalk tools register: Browser as: #browser. (MCWorkingCopy forPackage: (MCPackage named: 'NautilusRefactoring')) unload. "OK" #Nautilus asClass cleanUp. KMRepository reset. KMPragmaKeymapBuilder release. #NautilusUI asClass allSubInstances do: [ :inst | SystemAnnouncer uniqueInstance unsubscribe: inst]. Smalltalk garbageCollect. (MCWorkingCopy forPackage: (MCPackage named: 'NautilusCommon')) unload. (MCWorkingCopy forPackage: (MCPackage named: 'Nautilus')) unload. And now if does not work anymore. I get some TreePackage around. Apparently I get a weakMessageSend on classRemoved: and this message refers to an obsoletePackageTreeNautilus class. buildGroupManagerFor: anInstance | holder | holder := GroupHolder new. (holder addADynamicClassGroupSilentlyNamed: 'Most Viewed Classes' block: [ anInstance recentClassesElements ]) removable: false. (holder addADynamicClassGroupSilentlyNamed: 'Last Modified Classes' block: [ self lastModifiedClasses ]) removable: false. (holder addADynamicGroupSilentlyNamed: 'Work' block: [ {} ]) removable: true; isFillable: true. ^ holder Do you have any idea? A registration mechanism? from which I forgot to unregister. Stef