I prepped the walls in my home by removing wallpaper, and wallpaper glue with a mixture of vinegar and water. I then wiped down the wall with clean water. I mudded holes and cracks with drywall mud and primed. I painted over the primer and the paint bubbled. This happened in more then one room and I used different mud and paint in the two rooms. The walls are plaster and the house was built in the 1950's. Does anyone have a clue of have to fix this and/or prevent it in the future? Thanks