Erasing early gains, the Bombay Stock Exchange benchmark Sensex fell by over 68 points at noon today, on emergence of selling by funds following fresh developments on the political front. Sensex, which had gained over 131 points in morning trade, declined at 20,784 points at 1200 hrs as heavy-weight stocks led by Reliance Industries and State Bank of India declined sharply.The broad-based National Stock Exchange index Nifty, too, fell by over 24 points to 6,248 points at the same time.