Sounds like a solvent based adhesive to me, like contact cement. MEK works well, but use gloves and work outdoors (indoors it has a low flash point, so use it outside, no sparks please). Take a paper towel and soak it in MEK. Place it on the glue and leave there. It will evaporate fast, so do this a couple of times. This should work. If not, 3M adhesive remover from an auto shop works for this type of stuff.