Did you have the area re boarded? If so, its sounds as though there has not been a big enough gap between boards, so as boards contract and stretch, the crack appears. If it is just a hairline crack, then the previous advise is good.
Gently rub the glue with an artgum eraser. Use small, gentle strokes so you won't tear the paper. When the glue has been removed, wipe the area with a cloth dampened with clear water to remove any eraser particles. :D
