I figured this out. The error is occurring in section 15 of Form 8379. The numbers in column 1 are pulled from Schedule A (itemized deductions) and cannot be changed on Form 8379 but the total is shown in red. However, columns 2 and 3 are for the injured spouse and the spouse respectively. These numbers are not automatically filled in and are blank. As soon as I put the same numbers from column 1 into column 2 (all income and tax withheld/paid belong to the injured spouse in this case), the error went away.
So the red total in column 1 line 15G is for the sum of columns 2 and 3 from 15G, NOT because lines A thru F of column 1 do not add up. TT needs to be explained much better on that screen.
