Some years ago, I glued (liquid nail) 12"x12" cork tiles above our kitchen cabinet soffit. As time went by, Nana wanted to replace them with wallpaper. As you can guess, they came off in little pieces leaving the adhesive on the drywall. After tearing some of the drywall paper off, I realized I needed to stop what I was doing and dissolve the glue somehow. Here's the trick. I used a nice thick gelled paint remover to do the job at hand. After a couple of coats and a couple of hours, I used a dull putty knife and the liquid nail came off without leaving a mark in the surface of the drywall. It was ready for painting or papering.