Continuing to rise for the eighth straight session, the Sensex at the Bombay Stock Exchange gained 57 points, to 17,674, in early trade on Friday, on sustained buying interest by investors.But the Sensex later erased some of its gains, to stand a modest 22 points, or 0.1 percent in the green, at 17,638, a short while ago.Other Asian bourses in Japan, China, Singapore, South Korea, and Hong Kong were trading mixed, as concerns about US economic recovery offset easing worries about Europe's debt crisis