Norton Online Backup misses backups

I'm using Norton Online backup on 3 computers. Two computers work fine but on one computer the backup doesn't run automatically as it is set to do. It used to work fine but in the last week or so it has quit running. The only way to get a backup to go is to run it manually. Rebooting the computer has no effect.

 

I'm running Windows 7 Professional 32 bit and the internet connection is wired. The backup is set to run scheduled with the recommended automatic setting. I'm running the most up to date version. The icon in the system tray is a yellow circle with a black up and down arrow displayed.

 

Any thoughts on how to get the schedule going again?

 

Thanks.