Erasing all its initial gains, the Sensex at the Bombay Stock Exchange fell 136 points, or 0.7 percent, to a three-week closing low of 18,578, today. The Nifty at the National Stock Exchange lost 39 points, or 0.7 percent, to 5,648.But stock markets in Japan, Hong Kong, South Korea and Singapore rose between 0.1 percent and 1.4 percent.