Your installation medium contains a mix of both trusty and wily. You need to format a USB stick before reusing it for another distro/release.
** Changed in: grub-installer (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1518146 Title: Failed installation Ubuntu 14.04.3 on Acer E5-573g grub-efi- amd64-signed package could't be installed To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub-installer/+bug/1518146/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs