Given Marcello Foschi's "I have exactly the same problem booting Ubuntu" and Luis VIlla's "I'm seeing the same error", I think it's safe to call this confirmed.
** Changed in: initramfs-tools (Ubuntu) Status: Unconfirmed => Confirmed -- Boot failure: FATAL: Module unknown not found https://launchpad.net/bugs/21759 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs