unexpecter errors on some examples

some other example fail with the exact same traceback... I

    > believe the problem lies with the gtk backend, since the
    > same example runs fine with the WX backend.

Your error message suggests to me that you have an out-of-day CVS
copy, which is not surprising since sourceforge seems to have problem
staying current.

Grab another copy when you get the chance and let me know if you have
any more problems.