This is a user to user forum and nobody here can see your income tax return or your computer screen. So all we can do is make guesses. One guess is that you both entered a trade manually and imported the 1099-B containing that trade. Another guess is that you sold an ETF organized as a grantor trust or partnership and reported that sale using the Schedule K-1 interview AND that trade was also on a 1099-B you imported.
If you've really got a trade reported twice then delete one or the other of the trades. If you used the Schedule K-1 interview to enter the sale of an ETF then delete the broker's report of the trade as that 1099-B won't have the correct cost basis figure.
