[Moose-dev] Glamour tree presentation - red square of death

I am having some trouble with a with a tree presentation in Glamour being replaced with red square with a yellow cross. How can I attach troubleshooting this? Naively I tried wrapping each of the blocks passed with exception handling as follows.... ---- a tree updateOn: LEKShownClassesChanged from: self announcer when: [ :ann :entity | [ self setNavigatorIconsFor: LEKCimPackage rootPackage ] on: Exception do: [ self inform: 'upDateOn error' ] . true ] ; children: [ :item | [ item children sort: [ :before :after | before cimName < after cimName ] ] on: Exception do: [ self inform: 'children error' ] ] ; format: [ :item | [ item cimName ] on: Exception do: [ self inform: 'format error' ] ] ; act: [ :presentation :model | self shownClasses inspect ] entitled: 'selected package classes' ; icon: [ :item | [ self navigatorIconFor: item ] on: Exception do: [ self inform: 'icon error' ] ] ; ---- and also similarly wrapping the rendering... ---- GLMMorphicTreeRenderer>>render: aPresentation | container | [ container := super render: aPresentation. aPresentation shouldAllExpand ifTrue: [container submorphs first expandAll ]. aPresentation shouldRootsExpand ifTrue: [container submorphs first expandRoots ]. ] on: Exception do: [ self inform: 'render error' ]. Transcript crShow: container. ^ container ---- but nothing happens. Where does the red square get generated from? So I can try making a debugger come up instead of the red square. cheers, Ben