If I comment out all occurrences of "with self.__lock:" I then get the
same error in another part of the code:

C:\Python26\lib\threading.py:803: RuntimeWarning: tp_compare didn't
return -1 or -2 for exception
  return _active[_get_ident()]
Exception in thread Thread-4:
Traceback (most recent call last):
  File "C:\Python26\lib\threading.py", line 525, in __bootstrap_inner
    self.run()
  File "C:\Documents and Settings\David\My
Documents\pyzui\pyzui\tileprovider.py", line 82, in run
    self.__tasks_available.acquire()
  File "C:\Python26\lib\threading.py", line 115, in acquire
    me = current_thread()
  File "C:\Python26\lib\threading.py", line 803, in currentThread
    return _active[_get_ident()]
OverflowError: can't convert negative value to unsigned long

Where self.__tasks_available is a threading.Condition.

If I comment out that bit, I then get the following error:

Traceback (most recent call last):
  File "C:\Documents and Settings\David\My
Documents\pyzui\pyzui\tileprovider.py", line 91, in run
    tile = self._load(tile_id)
  File "C:\Documents and Settings\David\My
Documents\pyzui\pyzui\dynamictileprovider.py", line 55, in _load
    tile_id, True, filext=self.filext)
  File "C:\Documents and Settings\David\My
Documents\pyzui\pyzui\tilestore.py", line 72, in get_tile_path
    prefix = get_media_path(media_id)
  File "C:\Documents and Settings\David\My
Documents\pyzui\pyzui\tilestore.py", line 46, in get_media_path
    media_dir = os.path.join(tile_dir, media_hash)
  File "C:\Python26\lib\ntpath.py", line 97, in join
    if path[-1] in "/\\":
IndexError: cannot fit 'int' into an index-sized integer

I'm not sure if this error is related to the other errors, but similarly
this error only occurs in this specific thread.