The traceback looks like wsgiref.close() was called before handle_error() was called (perhaps for a second time?)

We'll probably need a reproducer (as simple as possible please) to debug this further, which might be difficult since it may be tricky to simulate the windows error.  But you might also want to, say, post to python-list and see if anyone can spot a problem with your code.  Could it be that it is calling wsgiref.close at the wrong time?