If you came across this error after upgrading the Plesk control panel or for any other reason then don’t panic as this can simply be resolved by following the below simple steps ::
Login to any other Plesk server and take a dump of the BackupsScheduled table
mysqldump psa BackupsScheduled > BackupsScheduled.sql -u admin -p`cat /etc/psa/.psa.shadow`
and once you have the .sql backup of the BackupsScheduled table then download the .sql backup file on the server where you are getting the error “Table ‘psa.BackupsScheduled’ doesn’t exist” and restore it .
mysql psa < BackupsScheduled.sql -u admin -p`cat /etc/psa/.psa.shadow`
Finally restart the MySQL service and you are done.