OS won't install

[yesbruce]

error report that GRUB won't install when upgrading OS

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.6 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.13.0-36.40~16.04.1-generic 4.13.13
Uname: Linux 4.13.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
CasperVersion: 1.376.2
Date: Sun Mar 11 13:27:41 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu-mate.seed boot=casper only-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu-MATE 16.04.4 LTS "Xenial Xerus" - Release amd64 (20180228)
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Phillip Susi (psusi)]

Your disk is currently partitioned to boot in bios mode, but you booted the installer in EFI mode. A warning message prompted you that this could be a problem and recommended performing a bios mode install instead, but you chose not to. You either need to perform the bios mode install, or partition the disk using GPT and set up an EFI system partition to install in EFI mode. This will be done for you if you choose the "use entire disk" guided install option.