Professor Gabriel J. Chin of the University of Arizona wrote the analysis suggesting that McCain's birth in the Panama Canal Zone while his father was on active military duty qualified him as a citizen under a law later enacted by Congress, but didn't make him a "natural-born citizen," which is what the Constitution requires for the presidency.
This issue has been kicking around constitutional circles for a while, and Chin's opinion is decidedly a minority view. Indeed, earlier this year "the Senate approved a nonbinding resolution declaring that Mr. McCain is eligible to be president. Its sponsors said the nation's founders would have never intended to deny the presidency to the offspring of military personnel stationed out of the country."
That's almost certainly true. But it may be a tougher argument for McCain to make now that he's devoted to "strict constructionist" interpretations of the Constitution.
After all, if you start messing with the language of the Founders, next thing you know, you've got a constitutional right to privacy, and we can't have that, eh?