This site has a good summary of the debate. Peiser failed to replicate Oreske's study, instead he came up with a different study that gave different results. I haven't seen any explanation why he changed the study. Best reply is from Oreskes:

"I stand by my work, which was published in a peer-reviewed refereed journal--indeed, one of the leading peer reviewed scientific journals in the world. If Mr Peiser has something that he thinks contributes to the discussion, then he should do the same--submit it for peer review, rather than trying to have the issue adjudicated in the mass media."

(Peiser had submitted a letter, not a study for peer review.)