Cannot Unlock the Screen I ran into the issue of not being able to log back in after locking my screen. I would have to use the switch user option and re-login. After a quick search, here is what I found:

sudo chown root:shadow /sbin/unix_chkpwd
sudo chmod 2755 /sbin/unix_chkpwd

Run these two commands and all should be well.

You can also try these if the first two don't work:

sudo chown root:shadow /etc/shadow
sudo chmod 440 /etc/shadow

– Main.FredPettis - 12 Dec 2008