Fatal error: Uncaught Error: Call to undefined function wp_json_encode() in /home/ioscotland/public_html/wp-content/plugins/cornerstone/includes/views/admin/forms/multi-select.php:10 Stack trace: #0 {main} thrown in /home/ioscotland/public_html/wp-content/plugins/cornerstone/includes/views/admin/forms/multi-select.php on line 10