How do I backup ReadyNAS to external USB?

Thanks, Netgear. I really appreciated losing the post I wrote when I needed to reset my password. I also appreciate the amazingly detailed instructions for backing up my ReadyNAS...

So how do I back up my ReadyNAS to an external USB drive? I have a drive plugged into the front USB port of my ReadyNAS NV+. In Frontview, I have selected "Volume: c" for the source and "USB Device (Front Port) for destination. But when I start the backup, I get an error message saying "The backup destination is a non-existent local share."

I would appreciate it if someone would walk me through this, because it shouldn't be that hard.