I am seeing this issue lately. I initialize mongodb connections within the fork.
Could the connection pool be getting overloaded and closing connections?

Error Log:

File "/opt/py26/lib/python2.6/site-packages/pymongo/cursor.py", line 606, in next
if len(self.__data) or self._refresh():
File "/opt/py26/lib/python2.6/site-packages/pymongo/cursor.py", line 569, in _refresh
self._query_spec(), self._fields))
File "/opt/py26/lib/python2.6/site-packages/pymongo/cursor.py", line 526, in __send_message
**kwargs)
File "/opt/py26/lib/python2.6/site-packages/pymongo/connection.py", line 788, in _send_message_with_response
return self.__send_and_receive(message, sock)
File "/opt/py26/lib/python2.6/site-packages/pymongo/connection.py", line 769, in __send_and_receive
return self.__receive_message_on_socket(1, request_id, sock)
File "/opt/py26/lib/python2.6/site-packages/pymongo/connection.py", line 759, in __receive_message_on_socket
struct.unpack("<i", header[8:12])[0])
AssertionError: ids don't match -43280947 0