Cf.
#529,
#530 &
#531 for more context
.
I you're using the latest release of USBNet, the usbnet error mesage probably stems from the fact that you're booting the device while it is plugged in. Don't. Plug it in just after ssh starts (which should be right around the time the spinner disappears, in case you haven't setup usbnet in verbose mode, and thus don't have the eips print to guide you).