This fix typically works if:

1. Multi Monitor Wallpaper Wallpaper won’t set for a screen
2. Wallpaper is lost/broken when you attach or remove monitors

What to do

• Open Multi Monitor Wallpaper
• Open settings (click on the cog icon, or menu/Multi Monitor Wallpaper/preferences)
• Click on ‘Reset All Wallpapers’
• Allow the app access to the required folder

This will reset all your spaces/desktops (though you won’t immediately see the change in your currently visible workspace)

• Once you have done this, you can set your wallpapers with MMW again

Background for the Technically Minded

Setting the wallpaper is actually a very simple command in Mac OS. Essentially – I say ‘set this image for screen N’

Once that is done – Multi Monitor Wallpaper has no part in ‘keeping the wallpaper active’ – the operating system is completely in charge.

This means that when the wallpaper is ‘lost’ – the operating system failed to properly save and restore the configuration.

In some cases, the system gets ‘stuck’ and stops allowing apps like Multi Monitor Wallpaper to set new wallpapers.

I have pinned down at least one way to reliably re-create this bug on my mac. What seems to happen is that the database where the system stores what image is applied for each screen/space gets corrupted.

• The database is stored at ~/Library/Application Support/Dock/desktoppicture.db
• I have reported this to Apple (and submitted a demonstration project and corrupted database