$this->error(new XenForo_Phrase('please_enter_valid_callback_method'), 'cron_method');
$this->error(new XenForo_Phrase('please_enter_valid_callback_method', array('class' => $class, 'method' => $method)), 'cron_method');
And well, of course the phrase needs to be updated, that would reduce the hunting time down on misbehaving add-ons
Today, whenever I try to install an add-on that has a missing class, it says "Please enter a valid callback method" and leaves me hunting down whether it meant the installer, an add-on, a cron job, etc.
And this usually happens whenever it works perfectly on non-case-sensitive OS and then the add-on is installed on a case-sensitive OS and suddenly it cannot find one file.