"Installation Failed! Unable to mount boot partition" on a clean ATV1

I changed HD on my ATV1 , and installed from scratch the OS.
No file on the ATV1, no sync, nothing.
Ethernet cable.
I created the USB with aTV Flash Silver 4.6.
I plug USB in ATV1, than turn it on.
After FC logo, the scroll bar runs for some seconds, then stops saying:
“Installation Failed! Unable to mount boot partition”

Anyone has suggestions on how to solve it?