Are you using CloudBerry Backup or Explorer?

Just to clarify: If you're using the Schedule Backup menu option in Explorer, then you need CloudBerry Backup installed, as that feature simply starts an instance of that product. As far as the 404 issue, I'd recommend you send logs to the Support team via the Help - Send Feedback menu option. Thanks.

I was wanting to use CloudBerry Explorer with B2 Cloud. I'll try to install CloudBerry Backup and see if that helps resolve the scheduling issue. Thanks!

If you need backup, then you need CloudBerry Backup, not Explorer. Explorer is for file management, not backup. You can download a trial from the web site here: https://www.cloudberrylab.com/backup.aspx