It has most likely been caused by applying a thick, heavy coat of un-thinned paint to a textured or embossed surface. ‘Mud cracking’ can also be caused when the air temperature drops rapidly after applying a water-based product, or when over coating an emulsion without leaving sufficient drying time. The solution? Applying one or two thin coats will sometimes fill the cracks. Otherwise the best solution is to strip the surface, repaper and paint.