Screen locking issue

[Aurélien]

When locking the screen on xubuntu 16.04.1 with super+l (flag + l) the computer crash and a forced reboot is needed (holding the start button). This problem appeared after the upgrade from xubuntu 14.04 to 16.04

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-screensaver (not installed)
ProcVersionSignature: Ubuntu 4.4.0-34.53-generic 4.4.15
Uname: Linux 4.4.0-34-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Aug 27 10:42:21 2016
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-11-28 (272 days ago)
InstallationMedia: Xubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
ProcEnviron:
 LANGUAGE=fr_FR
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-screensaver
Symptom: security
Title: Screen locking issue
UpgradeStatus: Upgraded to xenial on 2016-08-23 (3 days ago)