Hi There,
Thank you for writing in, your version of X and Cornerstone is not compatible. Please do this:
On your admin dashboard navigate to Plugins panel, deactivate and delete your current Cornerstone (v1.3.3). Then navigate to X panel (wait for a few seconds)
Then navigate back to Plugins panel and you’ll see that the Cornerstone has been re-installed as version 2.1.7 (this is the version that is compatible with your current X)
Remember to clear all caches (plugin, server-side, CDN, and browser’s cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
But that is not the latest versions of X and CS though, the latest version of X is 6.0.4 and Cornerstone is 3.0.4. You can update to the latest versions if you want to.
Updating Your Themes and Plugins
Actually, I would advise updating to the latest version because you already have the latest version of Wordpress.
Hope it helps,
Cheers!