Yeah, dry icing sheets won't stick to dry icing. Icing sheets have sugar in them, so you only need to slightly moisten them (or the icing) to dissolve some of the sugar and make them tacky enough to stick. I usually use corn syrup to stick down frosting sheets; it spreads more evenly than thicker royal icing, and so you tend to get less lumpiness this way. However, be careful not to get the paper too damp, or the paper can buckle or dissolve and not stick in those areas - which is what sounds like happened to you. Best of luck!