Assuming that this is an Illinois state return, there must be an issue with the secondary taxpayer's signature requirements -- not the first taxpayer listed on a married return, but the second taxpayer listed.
This rejection can occur when the signature information you input in your Illinois e-file agreement doesn't match what's on file with the state's Department of Revenue.
Please see the TurboTax Help article “Illinois e-file rejects IL1040-8000-2 or IL1040-9900-2: Correct taxpayer's signature requirements” for more information and guidance.