Stocks weakened in late trading Tuesday. Blue chips were near their session lows, while broader indexes turned firmly lower. The Dow Jones industrial average dropped 0.6%, wiping out just about all of Monday's move. The Nasdaq and S&P 500 fell 0.3% each. Both hugged the flat line earlier. Volume continued to track lower across the board. Aruba Networks (ARUN) gapped down and tumbled 10% in big volume after delaying its 10-K filing. The software