After wavering all day, U.S. markets ended the day with losses.

Stocks waffled between small gains and losses ahead of the Federal Reserve's policy statement at 2:15 p.m. The Fed said the economy is weakening, but it didn't promise any new action. Stocks turned downward after that.

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At the close on Wall Street on Wednesday, the Dow Jones industrial average was down 32.55 points at 12,976.13. The Standard & Poor's 500 index was off 0.29 percent to 1,375.32. The Nasdaq composite index was down 0.66 percent at 2,920.21.

Three stocks fell for every two that rose on the New York Stock Exchange. Volume was heavier than usual at 4.3 billion shares.

Early in the day, technical glitches at Knight Capital, which processes stock trades, sent some stocks swinging wildly. The New York Stock Exchange said it would cancel trades in six stocks that had unusual moves.

Some stocks moved dramatically shortly after the opening of trading. Wizzard Software, which closed Tuesday night at $3.50, shot above $14 in the first minutes of trading, according to data compiled by FactSet.

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Knight told its clients to send their orders away from its system and said it was reviewing the issue. Knight's stock closed down $3.39, or 32.82 percent, at $6.94.