Mi Schooltool dejo de funcionar Server Error

Al cargar la pagina de schooltool muestra esto:

Server Error

An internal server error has occurred. This most likely means that you have found a bug in SchoolTool. Please report it on the issue tracker.
Exception

SystemError: NULL object passed to Py_BuildValue

Traceback

File "/usr/lib/python2.7/dist-packages/zope/publisher/publish.py", line 137, in publish
  publication.afterCall(request, obj)
File "/usr/lib/python2.7/dist-packages/zope/app/publication/browser.py", line 46, in afterCall
  super(BrowserPublication, self).afterCall(request, ob)
File "/usr/lib/python2.7/dist-packages/zope/app/publication/zopepublication.py", line 213, in afterCall
  txn.commit()
File "/usr/lib/python2.7/dist-packages/transaction/_transaction.py", line 329, in commit
  self._commitResources()
File "/usr/lib/python2.7/dist-packages/transaction/_transaction.py", line 443, in _commitResources
  rm.commit(self)
File "/usr/lib/python2.7/dist-packages/ZODB/Connection.py", line 567, in commit
  self._commit(transaction)
File "/usr/lib/python2.7/dist-packages/ZODB/Connection.py", line 623, in _commit
  self._store_objects(ObjectWriter(obj), transaction)
File "/usr/lib/python2.7/dist-packages/ZODB/Connection.py", line 658, in _store_objects
  p = writer.serialize(obj) # This calls __getstate__ of obj
File "/usr/lib/python2.7/dist-packages/ZODB/serialize.py", line 422, in serialize
  return self._dump(meta, obj.__getstate__())

Modules

schooltool 2.8.5 (/usr/lib/python2.7/dist-packages)

schooltool.cando 2.8.2 (/usr/lib/python2.7/dist-packages)

schooltool.gradebook 2.8.4.1 (/usr/lib/python2.7/dist-packages)

schooltool.intervention 2.7.0 (/usr/lib/python2.7/dist-packages)

schooltool.lyceum.journal 2.8.2.1 (/usr/lib/python2.7/dist-packages)
Runtime

Python 2.7.6 (default, Jun 22 2015, 18:00:18) [GCC 4.8.2]

Linux javier-HP-EliteBook-2570p 4.4.0-31-generic #50~14.04.1-Ubuntu SMP Wed Jul 13 01:06:37 UTC 2016 i686 i686

Filesystem encoding UTF-8, preferred UTF-8