Simple fix on grub4dos:
title Ubuntu 15.04
find --set-root /path-to-casper/casper/initrd.lz
kernel /path-to-casper/casper/vmlinuz --ignore-floppies cdrom-detect/try-usb=true live-media-path=/path-to-casper/casper/ ignore_uuid boot=casper -- lang=us
initrd /path-to-casper/casper/initrd.lz
quiet
boot
Simple fix on grub4dos:
title Ubuntu 15.04
find --set-root /path-to- casper/ casper/ initrd. lz
kernel /path-to- casper/ casper/ vmlinuz --ignore-floppies cdrom-detect/ try-usb= true live-media- path=/path- to-casper/ casper/ ignore_uuid boot=casper -- lang=us
initrd /path-to- casper/ casper/ initrd. lz
quiet
boot