'zombie backup', how to kill them

[flupke]

last years I had created 1 automatic backup for a domain, it was a test. Since then I updated plesk a few times, I now get every 15min a error per email from the server ' Error is occurred during scheduled backup'. The backup doesn't appear in the schedule backup lift of that domain.

How can I erase those backup for ever?

NB: I stopped the backupmanager cron but still, it executes every 15min!

Thks!