Hi all, Having an issue with booting the latest version of Mountain Lion from an external hard drive. Work gave me a Mac Mini which hasn't been updated in a while (currently has 10.6.6), and it doesn't have enough space on the hard drive to update. So I have downloaded Mountain Lion from the Mac App Store, installed it on a partition of an external hard drive and when I go to boot from it (pressing down the option key when I restart the mac mini), I get the grey screen with a circle and a line through it. I'm a little confused! Is there something I need to do on the mac mini to resolve this and successfully boot Mountain Lion from my external hard drive?