It seems MODx is not currently installed, or the configuration file cannot be found.
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Did the config file get updated properly when you ran the upgrade? It should now be defining those three constants.
config.inc.php is still in manager/includes, maybe something with "MODX_BASE_PATH", "MODX_BASE_URL" or "MODX_SITE_URL"?
if (!defined('MODX_BASE_PATH')) define('MODX_BASE_PATH', $base_path);
if (!defined('MODX_BASE_URL')) define('MODX_BASE_URL', $base_url);
if (!defined('MODX_SITE_URL')) define('MODX_SITE_URL', $site_url);