Grub fails to install from ISO boot with existing Win10 install

[jhansonxi]

UEFI NextBook 11 tablet with Win10
Ubuntu 16.04 x86_64
Loopback ISO boot from Grub2 on USB Flash drive.
Ubuntu installer (after many rounds of fighting over partition editing with ISO mounted) completes most of installation only to have Grub install fail.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: ubiquity 2.21.63 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CasperVersion: 1.376
Date: Sat May 14 19:44:00 2016
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi boot=casper iso-scan/filename=/ubuntu-16.04-desktop-amd64.iso noprompt noeject
LiveMediaBuild: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
ProcEnviron:
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Phillip Susi (psusi)]

You appear to have had a temporary network failure that prevented downloading certain packages. Please try again, and you may wish to install with the network disconnected so that it does not try downloading anything.

[Launchpad Janitor (janitor)]

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