Problem moving site

I am in the process of moving my WordPress site to another server and am following the instructions and recommendations provided in the on-line documentation. I’ve moved the database and up=dated the wp-config.php file and have now uploaded the actual site files to their new location. I’ve switched wp_debug to ‘true’.
However, when I try to access the site, I get the following message:
Fatal error: Uncaught Error: Call to undefined function json_decode() in /var/www/html/Newsite/wp-content/advanced-cache.php:38 Stack trace: #0 /var/www/html/Newsite/wp-settings.php(95): include() #1 /var/www/html/Newsite/wp-config.php(91): require_once('/var/www/html/N...') #2 /var/www/html/Newsite/wp-load.php(37): require_once('/var/www/html/N...') #3 /var/www/html/Newsite/wp-blog-header.php(13): require_once('/var/www/html/N...') #4 /var/www/html/index.php(17): require('/var/www/html/N...') #5 {main} thrown in /var/www/html/Newsite/wp-content/advanced-cache.php on line 38

This seems to be associated with the WP-Optimize plug-in. Any help/suggestions appreciated.