I solved this with the help of some great TurboTax reps over the phone. The problem was this--and I would characterize it as an oversight in the TurboTax code: even though I was taking the standard deduction and TurboTax had not taken me through screens related to itemized charitable deductions, in the background it had automatically carried forward my list of charities from the prior year. Having those blank entries in the invisible background was causing this mysterious error. By going in and manually deleting those entries, it eliminated this error related to this year's $300 cash charitable donation credit for non-itemizers.
