Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/zope/app/generations/generations.py", line 494, in evolve
    manager.evolve(context, generation)
  File "/usr/lib/python2.7/dist-packages/zope/app/generations/generations.py", line 145, in evolve
    evolver.evolve(context)
  File "/usr/lib/python2.7/dist-packages/schooltool/cando/generations/evolve2.py", line 189, in evolve
    fixSkillScores(app, person)
  File "/usr/lib/python2.7/dist-packages/schooltool/cando/generations/evolve2.py", line 160, in fixSkillScores
    evaluations._history.pop(n)
  File "/usr/lib/python2.7/dist-packages/zope/keyreference/persistent.py", line 61, in __cmp__
    if self.key_type_id == other.key_type_id:
AttributeError: 'int' object has no attribute 'key_type_id'