can't install ubuntu16.04 to 32GB usb flashdisk

[solidblue]

I tried to install Ubuntu into a flashdisk which is external disk thou, but I couldn't be successfull.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.2
ProcVersionSignature: Ubuntu 4.4.0-31.50-generic 4.4.13
Uname: Linux 4.4.0-31-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CasperVersion: 1.376
Date: Wed Mar 1 00:35:14 2017
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[apt-ghetto (apt-ghetto)]

You had a network failure while trying to download packages. Please try again with either a working network connection, or no network connection at all.

I recommend to use a wired connection instead of wireless.

[Launchpad Janitor (janitor)]

[Expired for grub-installer (Ubuntu) because there has been no activity for 60 days.]