Hi, I showed Pharo to a friend and wanted to show the nice feature of fueling out an exception and then using FLMaterializer class>>#materializeFromFileNamed: to load it back and get a debugger up. In Pharo5 I am presented a DNU instead. The DNU is on GTGenericStackDebugger as it doesn't understand the message Fuel is sending. What to fix, Fuel to use the new protocol or GTGenericStackDebugger to honor the old protocol? FueldOutStackDebugAction>>#serializeTestFailureContext: aContext toFileNamed: aFilename | serializer | serializer := FLSerializer newDefault. self encodeDebugInformationOn: serializer. serializer addPostMaterializationAction: [ :materialization | Smalltalk tools debugger openOn: Processor activeProcess context: materialization root label: 'External stack' contents: nil fullView: false ]. So it looks like now it should create a debug session first and then pass it to the debugger? I think loading new fuel in Pharo3.x is still possible so maybe it is best to re-add that protocol? comments? holger