ubuntu instaler crashed

[Iskandar Herputra Wahidiyat]

when trying to install ubuntu the installer crashed.
executablePath : /usr/share/ubiquity/istall.py
package : ubiquity 2.21.63.4
problem type : crash
title : install.py crashed with AssertionError in_init_():Failed to mount the targer:/target
apportVersion : 2.20.1-0ubuntu2.10
architecture : amd64
casperversion : 1.376.2
distrorelease : ubuntu 16.04
duplicateOf : https://bugs.launchpad.net/bugs/1619755

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.4
ProcVersionSignature: Ubuntu 4.10.0-28.32~16.04.2-generic 4.10.17
Uname: Linux 4.10.0-28-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CasperVersion: 1.376.2
Date: Wed Mar 21 05:07:04 2018
InstallCmdLine: file=/preseed/ubuntu.seed noprompt boot=casper iso-scan/filename=/ubuntu-16.04.3-desktop-amd64.iso quiet --
LiveMediaBuild: Ubuntu 16.04.3 LTS "Xenial Xerus" - Release amd64 (20170801)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[Phillip Susi (psusi)]

It looks like you tried to shrink a windows partition and this failed because you had already mounted it, then somehow you did not create and format a partition to install Ubuntu on.