installation - Unknown keyword in installer: Ubuntu 11.04 boot from USB

I've just downloaded Ubuntu 11.04 (Haven't we all?) and created a bootable USB with my existing 10.04LTS installation. However, when I try to boot it it gives me a message similar to: Unknown keyword in installer. and leaves me at a boot:_ promt (which does not do anything)

Any solutions will be incredibly helpful, because I want to use new Ubuntu!

Maybe you are experiencing the same bug as in can't install with usb pen drive, SYSLINUX problem.