actually,now that i take a closer look,you are just missing a coulple commands. you need to chmod 0755 /data/local/flash_image
before you can ./flash_image misc /sdcard/mtd0.img
when you are doing the commands,look carefully at my codebox in post 1... yours will need to look like that.
if you have run thru all this once allready,you can possibly just boot to bootloader and provided everything you did was correct,and your PB31IMG is on the root of your sd card(not internal storage) then it will flash the downgrade RUU.
back to work,but ill try and keep watvching