Are you sure that's the issue? What is the exact error message? I would suspect that Windows just defaults to a black background if it cannot find the wallpaper in question.
Not exactly an error-message. Windows takes an age to log me on after I offer my password, and then when it does, I'm logged into a brand-new spanking-new profile, with an information-balloon at the bottom saying "Windows could not load your user-profile and has logged you on with a temporary profile, which will be deleted when you log out".
Am I sure that is the problem? No.
But the machine was working before I did that, and now it doesn't. The logic seems to be fit, and I haven't been up to any other mischief.