I don’t know why but it seems that in some release of Ubuntu, the software incorporated in it called “Startup Disk Creator”, a software used to create ONLY bootable version of Ubuntu, is not quite perfect.
Because when the operation of the software is finished, after rebooting the pc to load the Live version of Ubuntu installed in the USB, the operation will stop at the beginning of the loading of some file more precisely it will show the message:
SYSLINUX 3.63 Debian-2008-07-15 EBIOS Copyright (C) 1994-2008 H. Peter Anvin
Unknown keyword in configuration file.
boot:
_
At first I thought that it was some very complicated problem to solve but in reality it only require a few minutes, most likely less than 5 min to solve everything.
- First you need a pc to connect your just created USB drive with Ubuntu installed in it;
- Then you open the folder called syslinux which is in the root of the USB;
- Inside of it there is a file called syslinux.cfg. You need to open it (with a text editor) to edit some line of text inside of that file;
- Find the line “ui gfxboot bootlogo” and simply remove the “ui”;
- Save the file and repeat the operation of booting from USB;
- This time the USB drive should not create any problem.
The edited file of syslinux.cfg should look like this:
# D-I config version 2.0
include menu.cfg
default vesamenu.c32
prompt 0
timeout 50
gfxboot bootlogo
Source: how to fix unknown keyword in configuration file ubuntu usb boot
XiaoNoSekai 