I you use your Browser's FIND (or SEARCH) feature, and search for the word 'wallpaper', you'll find a few Posts that talk about your problem.
Here are a few of them. Some are directly related to our 'fix' and the others are related to the 'removal' and 'clean-up' process. DO read them all as you might find them useful. I'm sure there are more on the Forum but I'll leave that up to you to do.