I think it's referring to the sudoku TDD blog series that happened a few years back. Essentially, someone tried to implement a sudoku solver using TDD - and after several posts, never managed to finish. Peter Norvig then came along and wrote a short elegant implementation.

Some use this to say TDD - which has ties to agile - doesn't work. But most people conclude that TDD isn't a silver bullet and you have to know about your problem domain before diving in.

Here's someone elses' blog post which includes links to both sets of posts: http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-s...