Log in as an admin Remove the "plugintypes" data of mod/assign/db/subplugins.json Bump version.php Open a terminal and tail the apache error log. e.g. tail -f /path/to/apache2/error.log Trigger the upgrade process on the site (eg. by going to the admin page). But don't go through the upgrade process yet. Confirm that you get don't get any warnings on the upgrade page. Watch the error log. Confirm that you get an error log that indicates that " plugintypes " is not defined in the assign's subplugins.json file. Remove all the contents of the assign's subplugins.json file Reload the page. Confirm that you get don't get any warnings on the upgrade page. Check the error log. Confirm that you get an error log that indicates that the assign's subplugins.json is invalid. Go through the upgrade process Confirm that upgrade works without any PHP errors/warnings.