Best guess is the wall paper installer used a product called "siezing" to keep the glue from soaking away into the wall beneath. This happens on my jobs frequently. Best solutions is to wipe the wall down with a sponge and TSP or a paint thinner of some kind. Please wear a mask. Zinnsers BIN primer is the best because it has an alcohol base. But regular new construction primer should work well after removing the seizing and wall paper adhesive. Good luck on your project.