I work at a university and we have a few computer labs that we push specific wallpapers to depending on what events are going on.  We use group policy to push the wallpaper out and after checking RSOP on each machine, they are all getting the policy.  I can also go into HKCU\software\microsoft\windows\currentversion\policies\system and I verify that the correct path is there.  Every user can also access the network location that the wallpaper is stored in. (Not using UNC, but a shared network location) 

The issue is that about 30% of the computers are not showing the correct wallpaper.  They are instead using the wallpaper that is defined at HKCU\control panel\desktop which by default points to c:\windows\web\wallpaper\windows\img0.jpg.  On these 30% I verified that group policy is getting applied and that the correct entry is in the reg defined by gp.

So I decided to just delete that Wallpaper value in HKCU\control panel\desktop so the computers wouldn't reference it, but when I do that I get an all black wallpaper.  

One fix that I found was to tskill dwm /a and the correct background shows up.  I don't really want to run a script on login to do that every time someone logs in.

Also, one difference I found was on the working computers there was a binary value in HKCU\control panel\desktop called TranscodedImage that points to the correct network location.  On the computers that it is not working, the value is pointing to the local c:\windows\web\wallpaper\windows\img0.jpg.

I know I could just use gp to force the wallpaper value HKCU\control panel\desktop to the correct location, but that's adding another step when we want to change a wallpaper.

Any ideas?

Hi Grayson,

There is different behavior on Windows 7 and Windows 8 on desktop wallpaper. In Windows 7, when we log into the system, the cached wallpaper file will re-generated  automatically. But in Windows 8.1, if the wallpaper path didnt change, the cached wallpaper will not re-generate.

This problem can occur if a desktop wallpaper is applied through group policy and any of the following conditions exist:
The default theme applied doesn't explicitly define a desktop wallpaper
The user has never explicitly defined a desktop wallpaper
A classic theme is in use

After I deleted below file and log off/log on I can see the desktop wallpaper automatically changed:

%USERPROFILE%\AppData\Roaming\Microsoft\Windows\Themes\TranscodedWallpaper

This problem occurs if the Wallpaper registry value in HKEY_CURRENT_USER\Control Panel\Desktop is either missing or empty.

To fix this in machines that have already been deployed, you need to configure the above registry value with a non-blank value.

For more information, please read this thread:

https://social.technet.microsoft.com/Forums/windowsserver/en-US/0c36d7bf-4694-46e1-b408-d644111c0264/black-desktop-wall-paper-after-implementing-group-policy?forum=winserver