Glad to hear it worked. I would love to know why though...probably they changed something in their bootloader above my knowledge (not much to be honest).
Cheers!
I have had a similar problem to the one you are describing with a recently bought Vontar X3 box (which had a newish October firmware). I downgraded the firmware to the April one and then I was able to use multiboot from the SD card.
Hope it helps.