The S&P 500 erased its gains for the year on Wednesday as Wall Street reversed some of its recent year-end rally, with many investors expressing concern about the outlook for early 2012.The Dow Jones industrial average <.DJI> dropped 82.65 points, or 0.67 percent, to 12,208.70. The Standard & Poor's 500 Index <.SPX> dropped 10.40 points, or 0.82 percent, to 1,255.03. The Nasdaq Composite Index <.IXIC> dropped 24.73 points, or 0.94 percent, to 2,600.47.