The problem I have with Natural Law theory is the a priori assumption that even if Man's will is fallen, Man's intellect and reason is not fallen, except maybe fallen by way of disinformation. Thus, "Natural Law" leads to the conclusion that it is possible for fallen men to accurately and truthfully know, understand, and apply the "laws" of Creation, apart from the Creator - and thus eliminate any knowledge of said Creator as a necessity for properly understanding history, science, law, and ultimately creation itself. Antitheistic, rebellious "science" becomes "neutral", safe science, and antitheistic scientists become our trusted priests and prophets, leading the way through the wilderness to the Promised Land.
Or you get safe, antitheistic pablum like Stephen Covey's Seven Habits of Highly Effective People which is founded on the assertion that the universe is governed by "principles" and not by a Creator.
This is only one school of natural law theory. Other natural law theorists hold that natural law is a participation in divine law, and thus believe that any attempts to separate natural law theory from God will go astray. See Russell Hittinger's _The First Grace_.
I like this statement, although I don't necessarily find it much of a problem. The thing I thought of in reading this was the Jewish mystical tradition of the Tree of Life and the Sephora ie that God manifests himself in various ways, and that it is impossible for man to utterly know him completely and in total because of our fallen nature.
Not sure if that is what you were speaking to, but that was what popped up in my mind.