When you simultaneously go long and short in the same transaction with Interactive Brokers, they report the transaction as only one line in the trade history. This will cause Negative Shares and incorrect Profit/Loss when imported.
To fix this, please undo the last import by clicking on the UNDO button. From the Account menu, click Import Settings, and then check "Short/Long Convert", and press OK. This will break up any trades in which you go simultaneously long and short into two trades. Take note of the pop-up, and click Yes. Click OK to save the account settings. Now re-import.
If using UNDO is no longer practical because of too many edits, you can click on ALL Trades to temporarily close the Negative Shares error screen, then from the Adjustments menu, click Force Match.
Please be sure to verify your open positions. Force Match is a very powerful function that can radically change your trades - see: Force Match Trades
Before your next import, go to Import Settings on the IB account tab, and check "Short/Long Convert", then click OK.