Erasing early losses, the BSE benchmark Sensex was up by 13 points a short while ago, trading at 20,005 points. The stock markets lost over 40 points in the opening trade on emergence of profit booking at existing higher levels but were hovering around the 20,000 level.Similarly, the wide-based National Stock Exchange Nifty index was trading at 6,006 points, down by 5 points. In the opening trade, Nifty fell by 20.40 points to 5,991.30 points.