XLS importer crashes on reimport in timetable code

File "/home/menesis/.buildout/eggs/zope.publisher-3.12.6-py2.7.egg/zope/publisher/publish.py", line 132, in publish
  result = publication.callObject(request, obj)
File "/home/menesis/.buildout/eggs/zope.app.publication-3.13.2-py2.7.egg/zope/app/publication/zopepublication.py", line 207, in callObject
  return mapply(ob, request.getPositionalArguments(), request)
File "/home/menesis/.buildout/eggs/zope.publisher-3.12.6-py2.7.egg/zope/publisher/publish.py", line 107, in mapply
  return debug_call(obj, args)
Extra information: <schooltool.skin.flourish.zcml_content.FlourishMegaImporter_import.html object at 0xf65354c>
File "/home/menesis/.buildout/eggs/zope.publisher-3.12.6-py2.7.egg/zope/publisher/publish.py", line 113, in debug_call
  return obj(*args)
File "/home/menesis/src/schooltool/flourish/src/schooltool/src/schooltool/skin/flourish/page.py", line 68, in __call__
  self.update()
File "/home/menesis/src/schooltool/flourish/src/schooltool/src/schooltool/export/importer.py", line 1286, in update
  imp.import_data(wb)
File "/home/menesis/src/schooltool/flourish/src/schooltool/src/schooltool/export/importer.py", line 262, in import_data
  return self.process()
File "/home/menesis/src/schooltool/flourish/src/schooltool/src/schooltool/export/importer.py", line 645, in process
  self.import_school_timetable(sh, row)
File "/home/menesis/src/schooltool/flourish/src/schooltool/src/schooltool/export/importer.py", line 639, in import_school_timetable
  self.createSchoolTimetable(data)
File "/home/menesis/src/schooltool/flourish/src/schooltool/src/schooltool/export/importer.py", line 451, in createSchoolTimetable
  container[timetable.__name__] = timetable
File "/home/menesis/.buildout/eggs/zope.container-3.12.0-py2.7-linux-i686.egg/zope/container/btree.py", line 112, in __setitem__
  setitem(self, self._setitemf, key, value)
File "/home/menesis/.buildout/eggs/zope.container-3.12.0-py2.7-linux-i686.egg/zope/container/contained.py", line 554, in setitem
  raise KeyError(name)
KeyError: u'simple'

Thank you a lot!