Cannot modify desktop wallpaper

If, when you go to Properties -> Desktop on your machine, Desktop Wallpaper Browse button is greyed out and you can't change wallpaper, right-click on Start button, type in regedit and click OK to open your registry. Navigate to

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System

and delete Wallpaper key.

If Wallpaper key is not there, check the same location for ActiveDesktop folder. If it is there - delete it. Now restart the computer and it should work