Go back to your W-2 and check the box 5 and box 6 entries. The amount in box 6 cannot be more then 1.45% of the amount in box 5. Even if it is $0.01 more than 1.45% of box 5, the program will require a form 8959. If it is a few cents more then remove the amount of cents to remove the error.
Click on Federal on the left side of the online program screen
Click on Wages & Income
On the W-2 shown, click on the Edit/Add button.
If you have more than 1 W-2, check the entries on all the W-2's entered.