If its white mold between the bales, I wouldn't worry about it if feeding it.  We have had that problem before, usually in a stemmy type hay like sudan, or headed out wheat mixed with alfalfa.  As others said, it happens when the bales go in the wrapper crooked, or they are not uniform in diameter, or the tension is not set high enough between the bales.  I feel your pain if you intended to sell it.  It is hard enough to get folks around here that have never had wet hay to consider buying it even without the white mold.