xubuntu18.04 installatiion from USB pen failed

[gianfara]

I tried to install xubuntu 18.04 on a PC with preexisting Ubuntu 12.10, two partition on hard disk: I chose to use the partition with Ubuntu 12.10 to install the new OS

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.6
ProcVersionSignature: Ubuntu 4.15.0-29.31-generic 4.15.18
Uname: Linux 4.15.0-29-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
Date: Mon Aug 13 17:15:44 2018
InstallCmdLine: BOOT_IMAGE=/multiboot/xubuntu-18.04.1-desktop-amd64/casper/vmlinuz file=/cdrom/multiboot/xubuntu-18.04.1-desktop-amd64/preseed/xubuntu.seed boot=casper cdrom-detect/try-usb=true persistent persistent-path=/multiboot/xubuntu-18.04.1-desktop-amd64 noprompt floppy.allowed_drive_mask=0 ignore_uuid live-media-path=/multiboot/xubuntu-18.04.1-desktop-amd64/casper/ initrd=/multiboot/xubuntu-18.04.1-desktop-amd64/casper/initrd quiet splash ---
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)