Based on the screenshot you shared, the checkbox is for the Illinois EITC. The qualifications for the Illinois EITC are different than the qualifications for the EITC on the Federal return. You may qualify for the state EITC when you did not qualify for the Federal EITC.
The error condition is asking you to check the box so that it can be determined if you qualify for the Illinois EITC. If you do qualify, then your refund/balance due for your state will be affected. TurboTax is trying to be sure you are claiming every credit that you may be qualified to claim to get your best possible results.
Checking the box does no harm. It then allows the program to determine if you meet the qualifications for the state EITC.
To learn more, see the following information from the Illinois DOR:
How do I qualify for the Illinois EITC?
@dgsimm
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