Hi there,

Thank you for reaching out, and sorry for the inconvenience.

The issue is related to your hosting server. The backend editor encounters an error, but the frontend editor functions properly. Your hosting provider should be able to assist you. You may need to disable mod_security, or if you're using Cloudflare, try disabling Rocket Loader from the Cloudflare settings.

Note: I have tested your site in a local environment, and the backend editor works fine.

Thank you for your understanding.

Best regards