What does this error mean: invalid ELF header

The error means the objectify.pyd is not a valid shared library. You seem to have lxml compiled for different version of python from what you are running.

Guessing from the path, the fact that 'ELF' is an object (shared and executable) format used on unices and the package has -win32 in it's name you are probably trying to use windows build on linux.