Prerequisites As far as we are going to verify some really early errors and they happen BEFORE any access to database, it's important to ensure that the following settings are defined in the config.php file, before the require_once(... line: $CFG->debug = E_ALL | E_STRICT; $CFG->debugdisplay = true; With the patch not applied (or reverted) Delete mod/assign/db/subplugins.json Go to the site main page. Verify that you get a blank page. Verify that in the webserver error log you get a PHP Fatal error related to Call to undefined function current_language() . With the patch applied Delete mod/assign/db/subplugins.json Go to the site main page. Verify that now you get a exception in the web page. Verify that the error is not anymore about current_language() , get_docs_url() , s() or get_performance_info() ). Verify that the error is the real one, aka, it says: Debug info: Error code: generalexceptionmessage $a contents: Call to undefined function debugging() Stack trace: line 540 of /lib/classes/component.php: Error thrown line 471 of /lib/classes/component.php: call to core_component::fetch_subtypes() line 383 of /lib/classes/component.php: call to core_component::fetch_plugintypes() ... ... Note: Don't worry about the error above, it's being fixed @ MDL-65995