My return was finally accepted by the IRS (TT version = Mac, Premier). What worked for me, was to go back to the Step-by-Step Penalty Section. As per Cameron.Jo...

Update: Checking box c didn’t work: IRS rejection #3. Waiting now for TurboTax to fix this

Update: My premier desktop Mac version TurboTax wouldn't let me override IIA check box, so I checked box C at the top of the form, requesting that the IRS figur...

Although I am getting a large refund, my return was rejected x 2 due to the same issue described above. I'll try myactuary's solution next.