Fatal error: Call to undefined function wp_json_encode() in /home/u279705722/public_html/wp-admin/includes/misc.php on line 668
Rename your plugins folder to plugins-off
Then reinstall WP core files from a CLEAN download of WP.
Where can I find this folder?
The plugins folder is found inside wp-content.
Mika is suggesting that you download a fresh zip file of WP, unzip it, then using FTP or your hosts file manager, delete wp-admin (entire folder) and wp-includes (entire folder), and replace them with the files from the unzip.
Be careful NOT to do anything to the wp-content folder or the wp-config.php or .htaccess files — those have the site-specific stuff for your installation.
Please note: If you are not comfortable manually manipulating the files like this, you may not be ready to manage a multisite network.
It’s harder than single site WP, and yes, it requires you to edit files.
