Ok, this fail is happening because we're using python3 unicode strings to call the ANSI MessageBoxA function. A possible fix;

Encode strings before passing the MessageBoxA (ctypes.txt.diff attached)

Alternatively, calls could be made to the unicode MessageBoxW function, but someone who knows about ctypes / Win32 magic numbers would have to look at that.

(Inspiration take from this stack overflow question http://stackoverflow.com/questions/18164994/the-ctypes-wraps-messageboxa-example-didnt-work-in-python33)