the cause of this in MY case was that I filed an amendment to the 2019 Federal Tax I submitted via Turbo Tax. (the amendment has to be mailed in - you're not able to file an amendment on-line) Because my 2020 Federal Tax submission was being made with the "new" AGI, captured on my 2019 amendment- the IRS system was rejecting it. The IRS was only recognizing the original 2019 AGI on-line submission. Once I corrected the 2019 AGI on my 2020 Federal submission to match first AGI submitted on-line for 2019 tax year, and THEN resubmitted my 2020 Federal submission, it was accepted by the IRS 🙂
