Tax and Interest Deduction Worksheet: Line 2a principal res. - Enter the real estate taxes you paid on your main home. Total real estate taxes on line 2g should not be a negative amount?

Go back to the section in Deductions and Credits where you entered real estate taxes paid on your principal residence and check your entries. TurboTax is indicating that there was a negative number.

You can enter the taxes either in the Mortgage Interest section or the Taxes section, as long as they are not duplicated.