Log out when using GIMP

[Tran Duy Hung]

Hi all,

I have an annoyed problem today with GIMP. When I use GIMP's crop 
function to crop my photo, the system logs me out right after I left 
click to start cropping, so all my works are lost. This happens all the 
time.

I want to file a bug report but I don't think GIMP causes this issue. I 
have look at /var/log/syslog but there is no information there at the 
time the crash happened, and this is what in my xsession-errors log:

(polkit-gnome-authentication-agent-1:2491): GLib-CRITICAL **: 
g_variant_new_string: assertion `string != NULL' failed

(polkit-gnome-authentication-agent-1:2491): polkit-gnome-1-WARNING **: 
Failed to register client: 
GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name 
org.gnome.SessionManager was not provided by any .service files
** Message: applet now removed from the notification area
** Message: using fallback from indicator to GtkStatusIcon
** Message: applet now embedded in the notification area
[4605:4622:35618189:ERROR:backend_impl.cc(1186)] Critical error found -8
Failed to open VDPAU backend libvdpau_nvidia.so: cannot open shared 
object file: No such file or directory
Failed to open VDPAU backend libvdpau_nvidia.so: cannot open shared 
object file: No such file or directory


Are the above error logs helpful? Or is there any other log file that I 
can view to find out what causes this problem in Lubuntu?

Regards,
Hung