[ERROR] BackWPup log 18-jun-2014 10:00: Backup

The backups are working real fine!! But I get an errormessage everytime a backup is finished, saying that it could not delete an old backup. If I look at the directory, the old backup is deleted, so everything works just fine. Apparently it triggers an errormessage although it deletes the old backup.
Could you fix this?

https://wordpress.org/plugins/backwpup/