What category are you receiving this message on?
TurboTax transfers pertinent information into your 2021 return from 2020, in an effort to save you time. Examples of what transfers are employers, sources of income such as interest, dividends, etc. So if you re-entered any of those categories (or others that may have transferred), you may have an empty "ghost" form hanging out in your return. You'll just need to go into the category and delete the empty (or "ghost") form. That should clear up your error.
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
