Comment 1 for bug 792497

It just happened again: When I opened calibre and clicked on the "convert" icon my GNOME session crashed, leaving me with the login screen. Linux was fine and even preserved my open DSL connection.

I attach my auth.log and syslog, which seem to contain a few suspicious lines, such as:
* polkitd(authority=local): Unregistered Authentication Agent for unix-session:/org/freedesktop/ConsoleKit/Session2...
* gdm-session-worker[4652]: WARNING: Unable to load file '/etc/gdm/custom.conf'...
* gdm-simple-greeter[4649]: Gtk-WARNING: /build/buildd/gtk+2.0-2.24.4/gtk/gtkwidget.c:5687: widget not within a GtkWindow
* gdm-session-worker[4652]: GLib-GObject-CRITICAL: g_value_get_boolean: assertion `G_VALUE_HOLDS_BOOLEAN (value)' failed

Especially the assertion in the last line does not seem very reassuring to me but I have no idea what may have caused it. Grepping older logs shows, however, that this assertion was also logged on days when Gnome did not crash.