Ubuntu impossible to install: "unable to find a medium containing a live filesystem"

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http://askubuntu.com – Yes, I have read questions and answers with similar titles for this issue, which prevented me from installing Ubuntu for several MONTHS now, trying to figure it out. I have a MacBookPro with triple partition (one for Mac Snow Leopard, one for Windows 7, one for Linux) created with reFIT firmware (not BootCamp). I set up the system according to these instructions for reFIT: http://lifehacker.com/5531037/how-to-triple+boot-your-mac-with-windows-a... Now. There is a free partition ready to accept Linux into its arms, but Linux does not want to participate. Most answ ()