Assume you are referring to the 2017 AGI that you entered for your electronic signature on a 2018 tax return.
The IRS may not have the correct 2017 AGI for your SS number in their database.
If you filed the 2017 tax return late in 2018 or early in 2019 then the IRS will not have your AGI in their database. Try entering a 0 (zero) for the 2017 AGI. If that is also rejected then you will have to print and mail the tax return.
See this TurboTax support FAQ for the procedure to print a tax return for mailing when using the online editions - https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...
