Did you use the IRS non-fliers website to register for the stimulus? If so, the IRS filed a 2019 tax return with your name and Social Security number. Now that you are trying to e-file another 2019 tax return it is being rejected since the IRS has already received a return with your information.
See this TurboTax support FAQ for how to proceed - https://ttlc.intuit.com/community/tax-topics/help/stimulus-how-to-file-your-return-after-getting-rej...
