Comment 12 for bug 1243339

This is due to a change in lightdm 1.7.5 - the guest wrapper is now configurable and the Ubuntu package was not setting it.

The solution is to add a file into /etc/lightdm/lightdm.conf.d to set this, i.e.:

$ bzr diff
=== added file 'debian/50-guest-wrapper.conf'
--- debian/50-guest-wrapper.conf 1970-01-01 00:00:00 +0000
+++ debian/50-guest-wrapper.conf 2013-10-27 04:36:08 +0000
@@ -0,0 +1,2 @@
+[SeatDefaults]
+guest-wrapper=/usr/lib/lightdm/lightdm/lightdm-greeter-session

=== modified file 'debian/changelog'
--- debian/changelog 2013-10-16 02:54:44 +0000
+++ debian/changelog 2013-10-27 04:36:25 +0000
@@ -1,3 +1,10 @@
+lightdm (1.8.2-0ubuntu1) UNRELEASED; urgency=low
+
+ * debian/50-guest-wrapper.conf:
+ - Configure guest session wrapper to use
+
+ -- Robert Ancell <email address hidden> Sun, 27 Oct 2013 17:34:20 +1300
+
 lightdm (1.8.2-0ubuntu1) saucy; urgency=low

   * New upstream release:

=== modified file 'debian/lightdm.install'
--- debian/lightdm.install 2013-07-16 23:36:16 +0000
+++ debian/lightdm.install 2013-10-27 04:36:08 +0000
@@ -14,3 +14,4 @@
 debian/source_lightdm.py usr/share/apport/package-hooks
 debian/50-xserver-command.conf etc/lightdm/lightdm.conf.d
 debian/50-greeter-wrapper.conf etc/lightdm/lightdm.conf.d
+debian/50-guest-wrapper.conf etc/lightdm/lightdm.conf.d