Comment 70 for bug 645818

On Kubuntu 12.10 it still affect me.

However, the solution shown here worked for me:
http://askubuntu.com/questions/141311/unknown-keyword-in-configuration-file-boot-error-when-booting-off-a-live-usb
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The problem is that usb-creator depends on syslinux-legacy 3.63, and uses it to write boot up informations into USB, while the parameters "ui" can only be accepted by syslinux 4.05, which was installed on ubuntu 12.04.

A simple solution to solve everything is:

sudo mv /usr/bin/syslinux-legacy /usr/bin/syslinux-legacy.bak
sudo ln -s /usr/bin/syslinux /usr/bin/syslinux-legacy

And you can actually use syslinux 4.05 to write boot information into USB.
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