Desktop Background Image by script

We have an startup script running picks a random image from a pool and places it in %programfiles%\mycompany\dekstop.jpg

During logon we change the users desktop, poiting to this image.

However: The user doesnt see this image, but an other one.

The strange thing is: when the user wants to change the desktop image, in the preview window the correct image is shown.

Also, running "RUNDLL32.EXE USER32.DLL,UpdatePerUserSystemParameters 1" will fix the desktop imidiatly.

I added this in the login script, but that doesn't seems to have any effect.