[ubuntu] Installing Ubuntu on USB Stick fails

Hi there,
I'm trying to install Ubuntu (12.04 Desktop) on a usb drive (Patriot 32GB Tab), but having some trouble so far.

I created a separate Ubuntu Live Stick.
Started the Live Stick and tried to install on my Patriot usb drive.
I pre-partitioned the usb drive (4GB Swap, 28GB Root).
Installing seemed to work fine, but if I try to boot from the stick I just get a flashing "_" on a black screen and nothing else.

Has anyone an idea what went wrong?
Did I miss a step?

Best Regards
Keks