I was having issues with Cornerstone displaying changes as I worked on a page. As I was investigating the problem, I noticed that Cornerstone was not activated. I tried to activate it and received this error:
Plugin could not be activated because it triggered a fatal error.
Fatal error: Cannot declare class Cornerstone_Plugin_Base, because the name is already in use in /home2/stuartrowens/nodusdesign.co/wp-content/plugins/cornerstone/includes/utility/plugin-base.php on line 6
I restored my site from a backup and found Cornerstone still disabled and me still receiving the error.