The description of the Christian God is of one of two kinds, either one which is, as the description of Zeus or Odin, which is concrete enough that it becomes obvious no such entity matches the description. But even the IPU has meaning. The IPU is a construct which demonstrates that one can put together a description which violates no linguistic or logical rules, and yet which is never the less existentially impossible. There can be no existential being which has both the attribute of being invisible and the attribute of possessing color. Thus the IPU can exist as an abstract object, useful such discussions as the above, but as an existential , it is incoherent.
Nothing can exist which possess the combination of attributes described.
What Barry has done is an Argument Ad Elenchi. I don't see how your alleged conclusion follows. It is certainly possible to talk about the IPU, or Gandalf, or liberty or any other abstraction. The error occurs when a category mistake is made and an abstract object is alleged to have existential being. At that point, the concept decoheres since nothing which matches the description can actually be.