I found the cause for me was my entry error in the earlier charitable deduction worksheet. TurboTax had pulled over my charities for last year, but Without dollar amounts. I didn't notice that, so didn't enter this year's amounts, thereby saying I had donated $0 dollars. Of course, when I tried to claim the $300 at the end it did not match up. Went back, put in the amounts for this year's donations and the error was resolved.
