Lubuntu 18.04 Installation Failed

[Ming]

I tried to install Lubuntu 18.04 Final Beta. The installation failed.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.4
ProcVersionSignature: Ubuntu 4.15.0-13.14-generic 4.15.10
Uname: Linux 4.15.0-13-generic i686
ApportVersion: 2.20.9-0ubuntu2
Architecture: i386
CasperVersion: 1.393
Date: Fri Apr 6 20:15:02 2018
InstallCmdLine: file=/cdrom/preseed/lubuntu.seed boot=casper only-ubiquity initrd=/casper/initrd.lz quiet splash ---
LiveMediaBuild: Lubuntu 18.04 LTS "Bionic Beaver" - Beta i386 (20180405)
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)