rejected installation

[Alain Fichot]

End of installation message:
Le paquet grub-efiamd64-signed n' a pas pu être installé dans /target/.
En l'abscence du programme de démarrage GRUB, le sustème installé ne pourra démarrer.
Thanks for your help

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.14.12 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 4.18.0-15.16~18.04.1-generic 4.18.20
Uname: Linux 4.18.0-15-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CasperVersion: 1.394
CurrentDesktop: ubuntu:GNOME
Date: Mon May 27 16:11:55 2019
InstallCmdLine: BOOT_IMAGE=(loop)/casper/vmlinuz root=UUID=2FC3-67D5 maybe-ubiquity debian-installer/language=fr keyboard-configuration/layoutcode=fr iso-scan/filename=/ubuntu-18.04.2-desktop-amd64.iso boot=casper file=/cdrom/preseed/ubuntu.seed noprompt quiet splash --
LiveMediaBuild: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
ProcEnviron:
 LANGUAGE=fr_FR.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)