Hi, Briefly, when using the multiprocessing module, when exceptions are thrown, they need to be pickleable in order to propagate, since that is how multiprocessing passes information around. See http://stackoverflow.com/questions/8785899/hang-in-python-script-using-sqlal... and Python bug http://bugs.python.org/issue1692335 for background. I've reported bugs http://bugs.python.org/issue13751 and http://www.sqlalchemy.org/trac/ticket/2371 and http://psycopg.lighthouseapp.com/projects/62710-psycopg/tickets/90-psycopg-e... and http://bugs.python.org/issue13760 in this context. I've been reporting them as I came across them. I can produce a complete example if necessary, but I think the problem is pretty obvious. Let me know whether you require followup action from me. Specifically, do you want me to report a bug? See below the traceback I just ran into. Please CC me on all replies. Thanks. Regards, Faheem ******************************************************************* Process PoolWorker-1: Traceback (most recent call last): File "/usr/lib/python2.6/multiprocessing/process.py", line 232, in _bootstrap Process PoolWorker-2: Traceback (most recent call last): File "/usr/lib/python2.6/multiprocessing/process.py", line 232, in _bootstrap self.run() File "/usr/lib/python2.6/multiprocessing/process.py", line 88, in run self._target(*self._args, **self._kwargs) File "/usr/lib/python2.6/multiprocessing/pool.py", line 71, in worker self.run() File "/usr/lib/python2.6/multiprocessing/process.py", line 88, in run self._target(*self._args, **self._kwargs) File "/usr/lib/python2.6/multiprocessing/pool.py", line 71, in worker put((job, i, result)) File "/usr/lib/python2.6/multiprocessing/queues.py", line 366, in put put((job, i, result)) File "/usr/lib/python2.6/multiprocessing/queues.py", line 366, in put return send(obj) PicklingError: Can't pickle <class 'Boost.Python.ArgumentError'>: import of module Boost.Python failed return send(obj) PicklingError: Can't pickle <class 'Boost.Python.ArgumentError'>: import of module Boost.Python failed