by Ken Task.
Follow up ... there is an update to QuickMail block:
https://moodle.org/plugins/view.php?plugin=block_quickmail
Just tested on a 2.4 moodle. Manual backup ran without any errors.
Does your 2.4 indicate there is an update available for it? If not, then manually install the upgrade.
Fingers crossed, that will fix it! ;)
'spirit of sharing', Ken