Are you using a legitimate Minecraft account?: no / yes
yes
Are you using Java 8, 64-bit?: no / yes
yes
Did you add any additional mods: yes (detail) / no
no
Crash/latest log link (if applicable): link to log / not applicable
https://pastebin.com/rGBC6DLi
Help needed

The backup mod keeps saying backup failed, even though it was working a few days ago, what can I do to get it working again?

I've had several people with the same issue as you, but I haven't been able to figure out what causes it. For a temporary fix try deleting the file named Last in the backup directory for your world. That's the file causing the problem, although I don't know how it becomes corrupted.