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cPickle has problems loading instances of gtk gobject.GEnum classes. 
gobject.GEnum is a subclass of int. On the other hand pickle handles
those classes correctly. Since cPickle is meant to be a faster version
of pickle this needs to be consider a bug. 
To test run the following script:
import gtk
##import pickle
import cPickle as pickle
simple_types = (
 bool,
 int,
 long,
 float,
 complex,
 basestring,
 type(None),
)
d = vars(gtk)
for (i,j) in d.iteritems():
 if isinstance(j, simple_types):
 try:
 s = pickle.dumps(j, pickle.HIGHEST_PROTOCOL)
 obj = pickle.loads(s)
 except (ValueError, TypeError):
 print j, type(j)
If you replace cPickle with pickle then the script runs fine.