Causes 500 server error in WP3.5 (multisite) admin pages

As soon as I activate this plugin in WP3.5, I get a HTTP 500 server error for all admin pages (frontend keeps working). I have reproduced this problem on two independent multisite installations. Haven’t tried it on a single site install yet, hence “(multisite)” in the title.

http://wordpress.org/extend/plugins/add-from-server/