Ubuntu – Cron, xconf-query and Xubuntu 14.04

cronxorgxubuntu

I have updated my Xubuntu to the 14.04 version. Unfortunately, I am experiencing a problem.
I have a script, named earth, updating the wallpaper of my desktop. Here is the code

#!/bin/sh
nice -n 19 /home/hp/.xplanet/download_xplanet_cloudmap --debug=1;
nice xplanet -projection rectangular -geometry 1366x768 -window -num_times 1 -output /home/hp/.xplanet/images/earth.png;
# nice xplanet -geometry 1280x1024 -num_times 1 -longitude 15 -latitude 38 -output /home/hp/.xplanet/images/earth.png
# gconftool-2 -t string -s /desktop/gnome/background/picture_filename /home/hp/.xplanet/images/earth.png;
xfconf-query --channel xfce4-desktop --property /backdrop/screen0/monitor0/image-path --set "/home/hp/.xplanet/images/earth.png"
xfconf-query --channel xfce4-desktop --property /backdrop/screen0/monitor1/image-path --set "/home/hp/.xplanet/images/earth.png"
xfconf-query --channel xfce4-desktop --property /backdrop/screen0/monitorLVDS-0/workspace0/last-image --set "/home/hp/.xplanet/images/earth.png"

When I run the script in a terminal, it works. But, if I add the running of the script to crontab, with the command crontab -e and including the line

00,20,40 * * * * ( export DISPLAY=:0.0; sh /home/hp/.xplanet/earth )

it doesn't work.

Particularly, the commands with xfconf-query don't run. It worked in Xubuntu 12.04.