The Sensex at the Bombay Stock Exchange fell 78 points, or 0.4 per cent, to 17,629 in opening trade, this morning, on mild selling by funds, amid weak regional bourses. Later, the Sensex remained subdued, and stood 45 points, or 0.3 percent in negative territory, at 17,663 in afternoon deals, a short while ago.Key stock indices in Japan, China, Hong Kong, Indonesia, South Korea, Taiwan and Singapore were trading mixed, today.