grub2 failure on fresh install

[vensires]

I was installing Ubuntu from a USB disk. I have already Windows 10 installed on my disk, upgraded from Windows 7. When trying to install Ubuntu, everything went flawlessly until grub2 was trying to be installed.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63.2 [modified: lib/partman/automatically_partition/question]
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 Sep 21 11:59:21 2016
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed cdrom-detect/try-usb=true noprompt floppy.allowed_drive_mask=0 ignore_uuid boot=casper only-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
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)

[vensires (vensires)]

The first time I tried the installation, I hadn't checked the "Install updates" checkbox. The second time I tried, I did and everything went ok. The only side effect was that I lost the Windows 10 entry from the Grub list menu but this is another issue and was repaired by a boot-repair package.

[Phillip Susi (psusi)]

Your disk is currently partitioned to boot in bios mode, but you booted the 16.04 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.