Whitcomb’s Grounding Argument for Atheism and Reply by Rasmussen et al

I am quoting the abstract of these papers here, without comment pro or con, for interested readers who may wish to read the papers for themselves. Feel free to debate in the combox.
Whitcomb’s argument for atheism:

I’m going to argue that omniscience is impossible and therefore that there is no God. The argument turns on the notion of grounding. After illustrating and clarifying that notion, I’ll start the argument in earnest. The first step will be to lay out five claims, one of which is the claim that there is an omniscient being, and the other four of which are claims about grounding. I’ll prove that these five claims are jointly inconsistent. Then I’ll argue for the truth of each of them except the claim that there is an omniscient being. From these arguments it follows that there are no omniscient beings and thus that there is no God.

Reply by Rasmussen, Cullison, and Howard-Snyder:

Abstract. Dennis Whitcomb argues that there is no God on the grounds that (i) God is supposed to be omniscient, yet (ii) nothing could be omniscient due to the nature of grounding. We give a formally identical argument that concludes that one of the present co-authors does not exist. Since he does exist, Whitcomb’s argument is unsound. But why is it unsound? That is a difficult question. We venture two answers. First, one of the grounding principles that the argument relies on is false. Second, the argument equivocates between two kinds of grounding: instance-grounding and quasi-mereological grounding. Happily, the equivocation can be avoided; unhappily, avoidance comes at the price of a false premise.