The "Twig_Extension_Core" extension is not enabled

After installing Admin "Addon User Manager" plugin. Here's the site link: http://alldiesel.net/

Any help would be appreciate. Thanks.

Hi dion,
Have you set true for pages: process: twig: true in your user/config/system.yaml ?

Hi Dominique,

thanks for your reply. Yes, it is set to "TRUE".