Civi 5.13.5, Drupal 7.67.
A colleague tried to send out a mailing through CiviMail to a smart group that we have been using for a few months now.
She tried to send the email but received this error message (unfortunately she didn't send a screenshot, only this text)
Error Unrecognized value for setting 'flexmailer_traditional'
We do have flexmailer currently installed and enabled as I've been trying to get Mosaico to work for months (no success), but we have previously successfully sent out mass mailings on CiviMail while Flexmailer has been enabled, without receiving this error message.
The email is still listed on Mailings > Draft and Unscheduled Mailings (/civicrm/mailing/browse/unscheduled?reset=1&scheduled=false), with the status marked as 'Unscheduled'. It is not listed on the Mailings > Scheduled and Sent Mailings page.
Any idea on why this has happened, and how I can fix it and/or ensure that it doesn't happen in the future?
Thanks in advanced!