To summarize, the built executable seems to fail while interpreting a
file in my existing cx_Freeze installation (which it shouldn't even be
running, as far as I know) and ultimately raises this error:
AttributeError: 'module' object has no attribute '_fix_up_module'.
I think this is an issue between cx_Freeze and Python 3.4.1 - there was a Stackoverflow question about it . Apparently rebuilding cx_Freeze with Python 3.4.1 solves it. You can download an installer built with 3.4.1 from Christoph Gohlke's site: http://www.lfd.uci.edu/~gohlke/pythonlibs/#cx_freeze
Then re-freeze and it should be fixed. Anthony has plans to avoid this kind of incompatibility in cx_Freeze 5.