Can't boot from Kali's SD Card Image on my ARM ChromeBook

[htamayo]

Hi, I have a Samsung ARM Chromebook running on Chrubuntu 12.04 - I get rid off Chrome OS - but I would like to have installed on my SSD just Kali Linux for several reasons, so, I have followed this tutorial (http://mihirsingh.com/kali-on-chromebook/), everything seems OK on my SD, but when I try to boot from it I can't do it; my Chromebook is already in developer mode, after turn it on I press Crtl+U (and Ctrl+Shift+U as well, just in case "U" really means uppercase) but I can't boot from my SD, I don't get any message, after 15 to 25 secs I boot into Chrubuntu.

I have checked my SD Card with this commands:

-sudo cgpt repair /dev/mmcblk3 
-sudo cgpt show /dev/mmcblk3

and everything looks ok.

just I can't execute this command:

sudo crossystem dev_boot_usb=1

I thinks because crossystem should be a command that belongs exclusively to Chrome OS Kernel.

So my questions are:
1. How can I check or force to boot from my SD Card?
2. Is there anyway to check the integrity of the SD Card?
3. what other processes should I do/check in order to gain access from my SD Card?

regards

[Wo1f]

Make certain you have installed the developer-mode BIOS by running sudo chromeos-firmwareupdate --mode=todev in the terminal.