I've just downloaded ubuntu 12.04 and wanted to make a fresh install on my macbook pro, I followed the instructions given here http://www.ubuntu.com/download/help/...ick-on-mac-osx and when the operations are completed I get this result:

The disk you inserted was not readable by this computer

Obviously, when I restart the pc, it cannot find any bootable device.

Note I've tried using Lion OSX

Thank you very much for your help!