Upgrading your PHP version might be a requirement, when upgrading your WordPress to the latest version or any related plugins. My firewall tool recommended me to upgrade my WordPress, which I did, and I saw this warning message (below) with the website being down. I was proceeding PHP upgrade from version 5.6 to 7.4 using the MultiPHP Manager in Cpanel.

Warning: Use of undefined constant WP_CONTENT_DIR – assumed ‘WP_CONTENT_DIR’ (this will throw an Error in a future version of PHP) in /home/XXXXX/public_html/wp-includes/load.php on line 115

Let me get to the point straight. The error was occurred by the auto-generated PHP handler (ver 7.4) from .htaccess that was conflicting with another PHP handler (ver 5.6) that was running simultaneously in the server.

My old PHP handler looks like this:

# Use PHP56 as default
AddHandler application/x-httpd-php56 .php
<IfModule mod_suphp.c>
    suPHP_ConfigPath /opt/php56/lib
</IfModule>

My new PHP handler looks like this:

# php -- BEGIN cPanel-generated handler, do not edit
# Set the “ea-php74” package as the default “PHP” programming language.
<IfModule mime_module>
  AddHandler application/x-httpd-ea-php74 .php .php7 .phtml
</IfModule>
# php -- END cPanel-generated handler, do not edit

In my case, the upgrade from the MultiPHP Manager was generating the 7.4 PHP handler in the public_html folder, and my old PHP version 5.6 handler was already existed in the folder above public_html which is above the root directory. That was the reason it was causing the error. You can’t run multiple PHP handlers for a single website.

My solution was to simply remove (or rename if you don’t want to delete the file) the .htaccess file (PHP 5.6) from one level above the root directory. Now it works like a charm!