I heard about this and it actually took me longer than I thought to find it. Apparently this isn't the first time these two had a tizzy. All the articles that kept coming up in a search with the names "krugman" and "barro" were from 2009. Anyway, this is from last weeK
Barro: "Keynesian Economics vs. Regular Economics"
(then David Glasner responds)
Krugman: "Irregular Economics"
The best part is the opening paragraph of Barro: "What few know is that there is no meaningful theoretical or empirical support for the Keynesian position."
And if you're interested in 2009, Tyler Cowen seems to have most of the links.