What year? SS is on line 5 and in 2017 and earlier it's on line 20.
That's because they changed some OTHER income on your return. They either said you left out some income or changed the taxable amount of any 1099R for IRA or 401K on line 4b or for 2017 lines 15&16 . They increased your other income which is making more of your SS taxable.
