A frequently referenced quote by "tax law deniers" (Freedom to Fascism,Zeitgeist, et al) is that of Judge James C Fox.
“If you… examined [the 16th amendment] carefully, you would find that a sufficient number of states never ratified that amendment.” -U.S. District Court Judge, James C. Fox, 2003”
Though it is often cited as a 'ruling', in truth it was anecdotal and not a ruling at all.
The case was that of Sullivan vs U.S. The plaintiff asked a ruling against Bush for acting in violation of the constitution in regards to war powers.
Judge Fox, though he appears somewhat sympathetic in the transcript, indicates that historical, unchallenged practice tends to show an accepted interpretation of the constitution. He used the 16th Amendment as an example. He read somewhere that it was not properly ratified but that the passing of several decades makes that a moot point.
A more complete quote follows:
(Fox) … I have to tell you that there are cases where a long course of history in fact does change the constitution, and I can think of one instance. I believe I'm correct on this. I think if you were to go back and try to find and review the ratification of the 16th amendment, which was the internal Revenue, Income Tax. I think if you went back and examined that carefully, you would find that a sufficient number of states never ratified that amendment. … And nonetheless, I think it's fair to say that it is part of the constitution of the United States and I don't think any court would ever … set it aside. Well, I've seen that — I've seen somewhere a treatise on that. And I think it was — I think I'm correct in saying that actually the ratification never really properly occurred… Yet nonetheless, I'm sure no court's going to say that the 16th amendment permitting income is void for any reason, although I wouldn't mind filing for a rebate myself.
So the 16th amendment ratification question this was just a recollection by the judge that he read 'somewhere'. It was hardly a careful examination by the judge and definitely not a ruling.
(Ref: * Transcript from Sullivan VS U.S)