I'm getting the same kind of errors.
I'm using a lot of threads, and one of them throws this thread nearly everytime I close my program (by gtk.main_quit)

It seems that python sets every variable to None, and then wakeup sleeping threads, which then crash, as they try to work with the None variables

Exception in thread Thread-3 (most likely raised during interpreter shutdown):
Traceback (most recent call last):
  File "/usr/lib/python2.4/threading.py", line 442, in __bootstrap
  File "/home/thomas/Programmering/python/skak/0.7/lib/pychess/System/ThreadPool.py", line 49, in run
  File "/usr/lib/python2.4/Queue.py", line 89, in put
  File "/usr/lib/python2.4/threading.py", line 237, in notify
exceptions.TypeError: exceptions must be classes, instances, or strings (deprecated), not NoneType
Unhandled exception in thread started by 
Error in sys.excepthook