Can not unlock

[Fred]

When I try to unlock, it just shows the black screen again and then when I move the moues it shows the unlock dialog again.

I have to click on the "Switch user" button, then unlock from LightDM.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: gnome-screensaver 3.6.1-4ubuntu1
ProcVersionSignature: Ubuntu 4.0.0-4.6-generic 4.0.7
Uname: Linux 4.0.0-4-generic x86_64
ApportVersion: 2.17.3-0ubuntu4
Architecture: amd64
CurrentDesktop: GNOME-Classic:GNOME
Date: Sun Jul 12 18:24:59 2015
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session session-name 'ubuntu'
 org.gnome.desktop.session idle-delay uint32 1800
InstallationDate: Installed on 2013-12-26 (562 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
SourcePackage: gnome-screensaver
UpgradeStatus: Upgraded to wily on 2015-06-28 (13 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.