[CentOS] setting the screen background with gconftool-2

I centos 5 I can run this command:
su myuser -c "/usr/bin/gconftool-2 -t string --set 
/desktop/gnome/background/picture_filename 
/usr/share/backgrounds/images/mypic.png"

and this works fine.

under centos 6 it does not appear to be working...
I can run the similiar --get command and it tells me its set to what I 
asked for. However the screen is not showing mypic.png
I can use gconf-editor to set it manually and it works.
I looked to see if gconfd-2 is running and it is.

What might be happening that the screen is not changing and showing the 
actual pic?

Thanks,

Jerry