problem with USB elive distribution creation

[Prof. Privitera Giuseppe]

I extracted the elive distribution into the usb device and than i run 
the command

~$ grub-install --recheck --no-floppy --root-directory=/media/elive_5 
/dev/elive_5

as reported on this page:

http://www.elivecd.org/Help/Howto/boot-elive-from-usb

This is is the output error:

/usr/sbin/grub-probe: errore: cannot find a GRUB drive for /dev/sdb1.  
Check your device.map.
Auto-detection of a filesystem of /dev/sdb1 failed.
Please report this together with the output of "/usr/sbin/grub-probe 
--device-map="/media/elive_5/boot/grub/device.map" --target=fs -v 
/media/elive_5/boot/grub" to <address@hidden>

Note:
The USB filesystem used is ext4. May it be the problem?

Thanks, Giuseppe Privtera