I think it would be necessary to try another install. Since the 14 (exactly on 2016-01-21) I uploaded fixes to partman-prep which might well improve on the situation here.
The jist of it, at least, is that there already is a PReP partition being created on your system (the boot partition listed in your comment), except the flags might not be set properly on the device. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1523637 Title: grub-installer fails due to alternate disk partition error - 14.04.3 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub-installer/+bug/1523637/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
