while doing dual booting at last step of installation this problem has arised
ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.3 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.8.0-36.36~16.04.1-generic 4.8.11
Uname: Linux 4.8.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CasperVersion: 1.376.2
Date: Sat Aug 12 19:57:37 2017
InstallCmdLine: file=/cdrom/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash --- maybe-ubiquity
LiveMediaBuild: Ubuntu 16.04.2 LTS "Xenial Xerus" - Release amd64 (20170215.2)
ProcEnviron:
LANGUAGE=en_IN
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_IN
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)
Your installation medium is corrupt; you will need to create it and may want to verify it using the "check disc" option at the boot menu before installing.