maximizer - 1:05 am on Jun 6, 2012 (gmt 0)

I don't think it's anything to do with the unnatural links warning you got if your other pages are still ranking. If it's only the "new" pages, then a couple of my guesses:

1) the "new" pages are not being internally optimized well enough, e.g. not linked from the homepage, etc

2) the new pages have seen little to zero external links pointing to the page since it's creation

3) you are under-estimating the competition of those terms by expecting to just rank for them by putting up a new page of content targetting that term - I do believe domain authority does play a part out here when ranking for new internal pages and that's somewhere your domain might have suffered with the "unnatural links" warning, you'd need to re-establish some amount of authority