You could try to repartition it, using fdisk:
(unmount the USB stick first)
sudo fdisk /dev/sdX
- create a new partition table (not sure which command, enter "m" for
help)- I think it is "o"
- create new partition : n
- select type "primary" : p
- select number 1 : 1
- select default begin: just press enter
- select deafult end: just press enter
- write new partition table and exit: w
(just in case unplug and replug the USB stick, so the kernel uses the
new partition layout)
Then format the partition: sudo mkdosfs /dev/sdX1
Then you can follow the instruction from
http://www.pendrivelinux.com/install-grub2-on-usb-from-ubuntu-linux/
from the point 5 on.
Hope this helps.
MfG,
David