Erasing initial gains, the Sensex at the Bombay Stock Exchange closed with a marginal loss of 11 points, or 0.1 percent, at 18,507, today. The Nifty at the National Stock Exchange fell just 1 point, to 5,627.Stock markets in China, Hong Kong, South Korea and Singapore rose between 0.1 percent and 0.8 percent. MM/1730hrs