Can't unlock the screensaver

[Stefan Monnier <monnier@iro.umontreal.ca>]

Recently, my Debian stable system started to refuse my password when
I want to unlock my screen.

Most users on the system use Gnome 3 and their lock screen works OK
(thank god), but I use XFCE and xscreensaver and this one has recently
decided that it can't accept any passwords any more.

I tried it with other users (displaying their lock on my screen via an
"ssh -X" session), same result (it complains of failed authentication
and comes back asking for another password).

I tried to use gnome-screensaver instead (version 3.6.1-1), and the
result is the same: you can't unlock because authentication
always fails.

To the best of my knowledge, this problem may have started around the
same time that I changed the password of some user with `passwd'.

All other authentication mechanisms, like gdm, ssh, work just fine.

Any idea what might be going on?


        Stefan