Help building GUI with Tix

[infidel]

I am trying to build a GUI using the Tix module.  What I want is a
paned window with a tree in the left pane and a notebook in the right
pane.  I keep getting an error that I don't understand when adding
these widgets to the panes:

PythonWin 2.5.1 (r251:54863, May  1 2007, 17:47:05) [MSC v.1310 32 bit
(Intel)] on win32.
Portions Copyright 1994-2006 Mark Hammond - see 'Help/About PythonWin'
for further copyright information.
>>> import Tix
>>> app = Tix.Tk("Demo")
>>> panes = Tix.PanedWindow(app)
>>> panes.pack(fill=Tix.BOTH, expand=True)
>>> tree = Tix.Tree(panes)
>>> panes.add(tree)
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
  File "C:\Program Files\Python25\lib\lib-tk\Tix.py", line 1220, in
add
    self.tk.call(self._w, 'add', name, *self._options(cnf, kw))
TclError: bad window path name ".16442432..16442432"
>>>

What am I missing?

TIA