>>38

http://askubuntu.com/questions/671159/bootable-usb-needs-cd-rom
のように　まったく同じ　のページあるが
−−−−−−−−−−−
mount: mounting /dev/sda on /media failed: Invalid argument
unmount: can't unmount /media: invalid argument
mount: mounting /dev/sda on /media failed: Invalid argument
mount: mounting /dev/sda1 on /media failed: Invalid argument
unmount: can't unmount /media: invalid argument
mount: mounting /dev/sda1 on /media failed: Invalid argument
mount: mounting /dev/sda2 on /media failed: Invalid argument
unmount: can't unmount /media: invalid argument*
mount: mounting /dev/sda2 on /media failed: Invalid argument

−−−−−−
まったく同じ、と書いたが、本当に同じなのか気になってきた。インストーラ起動して、
再確認してくる。