I was helping a friend paint her hallway today and had a disaster. Her walls were wall papered. She took off the paper and washed off the glue. I sanded down the walls and wiped them down. Then we used a latex primer (Behr) over the original paint. I am fairly sure the original paint is latex. We had already done her kitchen 1 year ago and it was the same wall paper and paint underneath as what we encountered in the ajoining hallway today. Also we rubbed a spot with a cotton ball soaked in fingernail polish and some of the original paint did come off. However, the primer we used today clumped up on the wall and the roller would take off the paint you just put on. I am stressed!