I have been trying to perform a clean install on two 12400 chassis with no success. I am upgrading to R80.30 and have used the latest Polymorphic tool to build a bootable USB. I am not specifying any particular MAC, it should install on any machine. I have rebuild the USB several times an am confident it is correct. I am following the direction for clean install for this unit. I interrupt the boot process and perform a default reload. Once the system is reloaded, I begin the first time configuration wizard where I select the option to do a clean install from USB. I insert the USB and the system reloads but does not boot from the USB.