Comment 1 for bug 1388850

Running from source on windows I get this traceback on windows:
Process PoolWorker-3:
Traceback (most recent call last):
  File "c:\python33\lib\multiprocessing\process.py", line 258, in _bootstrap
    self.run()
  File "c:\python33\lib\multiprocessing\process.py", line 95, in run
    self._target(*self._args, **self._kwargs)
  File "c:\python33\lib\multiprocessing\pool.py", line 80, in worker
    task = get()
  File "c:\python33\lib\multiprocessing\queues.py", line 362, in get
    return recv()
  File "c:\python33\lib\multiprocessing\connection.py", line 252, in recv
    return pickle.loads(buf.getbuffer())
  File "c:\python33\lib\site-packages\sqlalchemy\orm\state.py", line 257, in __setstate__
    state_dict['manager'](self, inst, state_dict)
  File "c:\python33\lib\site-packages\sqlalchemy\orm\instrumentation.py", line 364, in __call__
    self.class_)
sqlalchemy.orm.exc.UnmappedInstanceError: Cannot deserialize object of type <class 'openlp.plugins.songs.lib.db.Song'> - no mapper() has been configured for this class within the current Python process!