I tried repeatedly to file and ran into this same issue. My father passed away last year and I was trying to file their return for 2020. Came across another thread related to 2019 filings in the forum that referenced FreeTaxUSA as the only vendor to successfully submit an efile, others had claimed H&R Block also rejected their repeated efiles. I did not want to force my mom to have to deal with signing and sending in a bunch of forms, so in the middle of the night, I decided to hop over and try to refile with FreeTaxUSA. Note that I did that only after looking up reputable reviews, https://www.pcmag.com/reviews/freetaxusa-2021-tax-year-2020 . I've been using TurboTax for over 10 years, I am not happy that they can't figure this issue out. Particularly in light of the fact that the cost for additional states increases every year. It was a heckuva lot cheaper for the other vendor even with two states and the federal efile. Granted, I doubt that I would feel crazy about doing a complex return without the brand name recognition, but in their FAQ they claim to have filed over 43 million returns. Regardless, if it simplifies my mom's life for filing and saved me money in the process, I can't complain. TurboTax needs to step up its game. I have been paying a larger and larger premium every year and this kind of thing is unacceptable. Good luck to anyone dealing with a similar situation, I know it is frustrating.
