Same! I entered "0" and it was accepted. "0" is apparently what you need to enter if you filed a late return last year, since the IRS AGI database records your AGI as of the previous year's April 15th deadline. So if you hadn't filed by that day, then their database would have originally recorded "0," even if you later submitted a return. It would definitely be nice if TurboTax would mention this important little nugget on the Previous Year's AGI screen to warn customers that if they filed late or had extensions the previous year that their AGI according to the IRS might be 0. That would have saved a lot of time and stress!
