Problem with boot from USB installing Ubuntu 12.04

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http://askubuntu.com – I'm trying to install ubuntu 12.04 using USB. After downloading the ISO file, I used pendrive to make bootable USB drive but after restarting my computer, I encounter this error: Unknown keyword in configuration file: ... vesamenu.c32 : not a COM32R image boot: I need your help as soon as possible. (HowTos)