Wittgenstein&ianism

I've been participating in philosophical small talk at a place called https://www.facebook.com/CafedieGalerie

To structure our talks a bit, we more or less tried to follow the book Think by Simon Blackburn. We didn't really advance a lot and didn't quite stick to the book.

While rereading it, I found a curious discussion of Saint Anselmo's and Descartes' Ontological Argument, in which Blackburn says that the real problem is the difficulty to compare the properties of imagined entities with real, not only imagined entities.

But the real difficulty for the argument is of course the one Kant says, followed up by Frege (and not, as Blackburn maintains, shown by quantification): What the fool gets by hearing about the most perfect being is the concept of such a being. But there is no way to conclude from there that there is an entity falling under such concept.

I can not imagine any way to get around this problem. So everything else strikes me only as a distraction from the main point. It´s hard to believe Blackburn shouldn't have seen that. What could be his point here?