Thanks for your quick reply! I've already paid the TurboTax fee via debit card, so that shouldn't be a problem. My "File by Mail" instructions say "Your Michigan state tax return (Form MI-1040) shows no balance due or refund amount." Is that related to this issue? The "File by Mail" instructions also say "Your tax return - The official return for mailing is included in this printout.", but the only document included is the Schedule C form, which is just a copy of the form from my Federal return, as you pointed out. Am I misunderstanding something here?
