Hello: I just finished a bath like that. It could have easily been prevented: if someone had primed the walls with primer or even paint. What to do: Sand off of the edges of the wall board paper that is ragged. then mud the wall. Make sure the mud you use is very fresh with no lumps or pieces of paper in it. use a wide spackle knife. Sand off high spots and prime the walls.It will take a lot of work and you will probably have to put a light skim coat of mud on the wall. Next time you want to take off wall paper: use a paper tiger, a good solution of water and wall paper remover ( vinegar works too ) and pull the paper straight down the wall. Not out from the wall, but straight down. Sorry it won't be easy.