Backup my 143 MB database add schedule not sufficient permissions

I am trying to backup my database and files and am having a heck of a time getting the backup to run. Every time I +add a schedule, whether manual or automatic, I get a WP error claiming that “I do not have sufficient permissions to access this page.” I head back to my Backups plugin and the schedule is listed there as running, however, it never completes (just keeps spinning). I’ve changed the settings of the schedule, deleted and “run now” again, but nothing is working. I can’t update my plugins until I am able to create a backup. Please help!