Thank you for reaching out to us. I checked your setup and I see you're using an outdated version of X with the latest version of Cornerstone. This could be the reason. Always make sure to update both X and Cornerstone to the latest version to avoid such errors and potential conflicts. You can find the latest version numbers here: (http://theme.co/changelog/) Then you can compare them to what's installed on your site.
If you find anything to be out of date, you can review our update guide.
Let us know how this goes!