This looks like the image you're using the install may be incomplete or damaged:
May 5 13:46:10 ubuntu ubiquity: E: Failed to fetch cdrom://Ubuntu 15.04 _Vivid Vervet_ - Release amd64 (20150422)/pool/main/g/grub2/grub-efi- amd64-bin_2.02~beta2-22ubuntu1_amd64.deb Hash Sum mismatch Could you try to verify the image you downloaded with md5sum, download it again if it's incomplete, and try again? ** Changed in: grub-installer (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1451841 Title: Install fails with ESP and Ext4 partition To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub-installer/+bug/1451841/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs