Can't boot 10.10 from flash drive on Macbook Pro

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http://askubuntu.com – I can't boot 10.10 from my SanDisk cruzer flash drive on my Macbook Pro. I made my flash drive from http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-mac-osx. When I have the flash drive plugged in, I hold down alt when I restart, but nothing except Macintosh HD and a Recovery Drive (which isn't the flash drive) shows up. Any suggestions appreciated. Thanks. (HowTos)