Change Wallpaper with VBScript at Domain Login

Ok.  I've search EE and the internet for a way to change the desktop wallpaper with VBS.  I've found some code that claims to work.  One problem that users have reported is that the code will change the wallpaper, but it doesn't "execute" the change.  For example, I run the code, but nothing appears to have happened.  I open the desktop properties and find that my new wallpaper has INDEED been set, but it's not displaying.  I make a slight change in the properties, hit apply, and then it displays.  Other users have reported this, and the code that they were provided was said to correct that problem.  Almost like forcing a refresh on the desktop.  I have pulled that code, combined it with some that will identify the username, and executed it.  No refresh.  What am I doing wrong?

Here's the code:

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dim wshShell
dim sUserName

Set wshShell = WScript.CreateObject("WScript.Shell")
sUserName = wshShell.ExpandEnvironmentStrings("%USERNAME%")

Set oShell = CreateObject("WScript.Shell")
Set oFSO = CreateObject("Scripting.FileSystemObject")

sWinDir = oFSO.GetSpecialFolder(0)
sWallPaper = "D:\My Documents\DownLoad\" & sUserName & " - bkg.jpg"

' update in registry
oShell.RegWrite "HKCU\Control Panel\Desktop\Wallpaper", sWallPaper

' let the system know about the change
oShell.Run "%windir%\System32\RUNDLL32.EXE user32.dll,UpdatePerUserSystemParameters", 1, True

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By the way, I want to run this code only once.  I will call it from a login script.  I don't need to run it more than once.  So, if anyone can give me a good way to do that, I would appreciate it.  I have done this "run-once" type of thing before, but it is very un-elegant.