I have updated the checks performed on Adsense code pasted from Google's site into the skyscraper settings.
Some customers were reporting that Instant Sites was rejecting their unmodified Adsense code. This was because Google had updated the Javascript code ever so slightly causing are checks to fail.
So if you gave up trying to add Adsense code to your skyscrapers because of the error then you can try again and it should now work.