Comment 4 for bug 297409

This also affects Ubuntu server edition. I managed to get throught this issue by doing what was said in comment #3 and pressing tab when "default" was selected in unetbootin boot and pressing tab to add "cdrom-detect/try-usb=true" to that line. I found these instructions from http://blog.smalleycreative.com/linux/fix-for-ubuntu-10-04-server-usb-install/ .