[LightDM] lightdm login failure on 2nd a subsequent login attempt.

[Leo B. Freeman]

I am seeing the same problem. I installed
ubuntu-gnome-16.04.1-desktop-amd64.iso
on an Intel NUC6i5SYH with
Intel® Core™ i5-6260U CPU @ 1.80GHz × 4 and
Intel® Iris Graphics 540 (Skylake GT3e).
I then installed lightdm and xfce4 with the
Synaptic Package Manager. Local logins work fine with
GDM, LighttDM, GNOME and Xfce.

However, remote XDMCP login from a VcXsrv X server running
on a Windows 10 computer works only once for each boot up
of the ubuntu system. On the second and subsequent remote
login attempts, after entering the password and proceeding,
the screen flicker twice and returns to the login screen.

The syslog for the failing logins diverges from the good
login at:
Aug  1 18:44:44 nucunifi systemd[4395]:
    Startup finished in 24ms.
Aug  1 18:44:44 nucunifi systemd[1]:
    Started User Manager for UID 1000.
Aug  1 18:44:44 nucunifi lightdm[3177]:
    ** (lightdm:3177): WARNING **: Error activating login1 session:
    GDBus.Error:org.freedesktop.DBus.Error.NotSupported:
    Operation not supported
Aug  1 18:44:44 nucunifi lightdm[3177]:
    (lightdm:3177): GLib-GObject-CRITICAL **: g_object_unref:
    assertion 'G_IS_OBJECT (object)' failed
Aug  1 18:44:44 nucunifi systemd[1]:
    Started Session c6 of user lightdm.
Aug  1 18:44:44 nucunifi lightdm[3177]:
    ** (lightdm:3177): WARNING **: Error activating login1 session:
    GDBus.Error:org.freedesktop.DBus.Error.NotSupported:
    Operation not supported
Aug  1 18:44:46 nucunifi systemd[1]:
    Stopping User Manager for UID 1000...
Aug  1 18:44:46 nucunifi systemd[4395]:
    Reached target Shutdown.

Any ideas on how to get this to work?