1) I assume you installed Glade at glade4_win32 and set the environment variable %GLADE_HOME% to this dir, and %PYTHONPATH% so the same dir.
2) Do you have write permission to this directory? Is there the ui.py file in this directory, and is it readable?
3) Check that you are not running one version of Glade and pointing PYTHONPATH at another version of the ui.py file. This will also give the error you see.
Also I'd recommend downloading the latest 4.3.1 build, as there were a few issues with 4.2.7/4.3.0.