could be something else. here's a complete reason for the code
What happened IL1040-8000-2 - This return could not be processed for electronic filing by Illinois because of an issue with one or more of the pieces of information used to validate the signature: IL PIN, Prior Year AGI, Driver's License or State ID Number. IL1040-8600-2 - Please review and correct the Primary taxpayer's signature requirements. At least one of the following signature fields must be present and valid on the Dept. Of Revenue's file: IL PIN, Prior Year AGI, Driver's License or State ID Number.
if you use Il-pin delete the DL info. also if you're married each taxpayer has a different pin.
