Nonstop backup doesn't work!

Maybe it should be called "always stopped" backup.

I've started over a few times and I can create ONE successful nonstop backup, but it never works again, I have to manually restarted it and then it stops. I get no error or explanation as to why it's stopped and I'm very frustrated. I've restarted the service, checked to make sure Norton Firewall is allowing it, turned off Norton Firewall. What else can I do?

Windows 7; TI 2015 build 6613

I'm backing up to a network drive. Other types of backups to portable hard drives have worked fine.