To reproduce:

bash-4.0$ python
Python 2.6.4 (r264:75706, Aug 16 2010, 16:36:38) [C] on sunos5
Type "help", "copyright", "credits" or "license" for more information.
>>> import wnck
/usr/lib/python2.6/vendor-packages/gtk-2.0/gtk/__init__.py:57: GtkWarning: could not open display
  warnings.warn(str(e), _gtk.Warning)

** (.:4024): WARNING **: Trying to register gtype 'WnckWindowState' as enum when in fact it is of type 'GFlags'

** (.:4024): WARNING **: Trying to register gtype 'WnckWindowActions' as enum when in fact it is of type 'GFlags'

** (.:4024): WARNING **: Trying to register gtype 'WnckWindowMoveResizeMask' as enum when in fact it is of type 'GFlags'
>>> wnck.screen_get_default()
Segmentation Fault (core dumped)
-bash-4.0$ pstack core
core 'core' of 4024:    python
 fea89ed7 wnck_screen_get_default (14f, 0, 80479d8, fed590c0, 0, 0) + 1b
 feae9a80 _wrap_wnck_screen_get_default (0, 0, 80479d8, fed58d92) + 18
 fed590c0 call_function (8047a4c, 0, 8047a28, fed53206) + 33c
 fed56221 PyEval_EvalFrameEx (8417194, 0, 80941c4, 80941c4) + 3029
   [ <stdin>:1 (<module>) ]
 fed57cd0 PyEval_EvalCodeEx (8098770, 80941c4, 80941c4, 0, 0, 0) + 91c
 fed53102 PyEval_EvalCode (8098770, 80941c4, 80941c4, 80a39c8) + 32
 fed781ae run_mod  (81556b8, fee02184, 80941c4, 80941c4, 8047cac) + 3a
 fed76f72 PyRun_InteractiveOneFlags (fef737f8, fee02184, 8047cac, fed76c66) + 216
 fed76d46 PyRun_InteractiveLoopFlags (fef737f8, fee02184, 8047cac, fed76be6) + ee
 fed76c1c PyRun_AnyFileExFlags (fef737f8, fee02184, 0, 8047cac) + 44
 fed85694 Py_Main  (1, 8047dbc, feef4785, 8050b88, 10000, 0) + a94
 08050bdf main     (1, 8047dbc, 8047dc4, feffb8f4) + 63
 08050aed _start   (1, 8047e70, 0, 8047e77, 8047e82, 8047e92) + 7d