After updating the platform, I cannot access any users. Not even updating the existing ones. I put the site into debug mode and this is what I get everytime I try to edit or delete or unblock an user:
1 () JROOT/administrator/components/com_acymailing/compat/joomla.php:318
2 acymailing_isAdmin() JROOT/plugins/system/regacymailing/regacymailing.php:56
3 plgSystemRegacymailing->onAfterRoute() JROOT/libraries/src/Plugin/CMSPlugin.php:289
4 Joomla\CMS\Plugin\CMSPlugin->Joomla\CMS\Plugin{closure}() JROOT/libraries/vendor/joomla/event/src/Dispatcher.php:486
5 Joomla\Event\Dispatcher->dispatch() JROOT/libraries/src/Application/EventAware.php:111
6 Joomla\CMS\Application\WebApplication->triggerEvent() JROOT/libraries/src/Application/AdministratorApplication.php:454
7 Joomla\CMS\Application\AdministratorApplication->route() JROOT/libraries/src/Application/AdministratorApplication.php:171
8 Joomla\CMS\Application\AdministratorApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:293
9 Joomla\CMS\Application\CMSApplication->execute() JROOT/administrator/includes/app.php:61
10 require_once() JROOT/administrator/index.php:32