cann't unlock screensaver

[Oliver]

When I lock the screen (strg-alt-l) or the sreensaver locked the screen atomatically, I can't unlock the the screen by typing in the correct password. The Screensaver reports 'password not correct'.
I can only lock in to the existing session by chosing 'change user' and doing the lock in from there.
I'm using ubuntu 12.04 LTS.
The File shadow has the permissions witch are mentioned in BUG #34775. But the file is not in /etc/shadow, that does not exist. It is directly in /etc.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-screensaver 3.4.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-61.93-generic 3.2.55
Uname: Linux 3.2.0-61-generic x86_64
ApportVersion: 2.0.1-0ubuntu17.6
Architecture: amd64
Date: Mon May 19 15:01:59 2014
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session idle-delay uint32 600
 org.gnome.desktop.session session-name 'ubuntu'
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
MarkForUpload: True
SourcePackage: gnome-screensaver
Symptom: security
Title: Screen locking issue
UpgradeStatus: No upgrade log present (probably fresh install)
WindowManager: No value set for `/desktop/gnome/session/required_components/windowmanager'

[Launchpad Janitor (janitor)]

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

[K.Mani (sailormani)]

The bug is FIXED & can be closed
/sbin/unix_chkpwd & /etc/shadow permission changed.

[Oliver (oli3)]

Thanks a lot.
The hint /sbin/unix_chkpwd leadead me to Bug #353356, where I found the solution.

SOLUTION:
chown root:shadow /sbin/unix_chkpwd
chmod 2755 /sbin/unix_chkpwd
chown root:shadow /etc/shadow