Hi,
I just downloaded the gantry plugin + theme and installed both on a fresh local installation of Wordpress (I'm running MAMP on my Mac).
The plugin installation/activation ran smoothly.
After installing the theme (add new theme / select file / upload) the page refreshed and ended up on a Internal Server Error page.
There's absolutely nothing running except a basic fresh wordpress installation (4.3.1_it), Gantry framework and the Timber plug-in.
Any clue?