Ok, I've found the problem and fixed it, messy but necessary for debugging.
In Pier-ModelStructure -> PRChildren -> isVaildChild
isValidChild: aStructure
^ (PRPath isValidName: aStructure name)
and: [ aStructure parent isNil
and: [ (self includes: aStructure name) not
and: [ (self decorated canBeParentOf: aStructure)
and: [ (aStructure canBeChildOf: self decorated) ] ] ] ]
I changed to:
isValidChild: aStructure
|aBool|
aBool := true.
(PRPath isValidName: aStructure name)
ifTrue: [Transcript crShow: 'PRPath is valid']
ifFalse: [aBool := false. Transcript crShow: 'PRPath is invalid'].
(aStructure parent isNil)
ifTrue: [Transcript crShow: 'Parent is nil']
ifFalse: [aBool := false. Transcript crShow: 'Parent is not nil'].
(self includes: aStructure name)
ifTrue: [aBool := false. Transcript crShow: 'self includes structure']
ifFalse: [Transcript crShow: 'Does not include itself.'].
(self decorated canBeParentOf: aStructure)
ifTrue: [aBool := false. Transcript crShow: 'can be parent']
ifFalse: [Transcript crShow: 'can''t be parent'].
(aStructure canBeChildOf: self decorated)
ifTrue: [Transcript crShow: 'can be child.']
ifFalse: [aBool := false. Transcript crShow: 'can''t be child'].
^aBool
Hopefully this will help figuring out why the problem occures.
As this code stands, it seems to allow me to add pictures etc.