I think there is a problem with Turbo Tax. I had the same issue. I was rejected twice. Finally, I went to View > Forms and opened the Form 1040 (1040Sr) worksheet. In page 3, Tax Smart Worksheet item D it was adding $600 (tax from additional form 4972). I deleted the 600 and left the line blank. It removed the x from line 16 box 2. Then closed the form, reviewed the taxes again and submitted one more time (it added the $600 to the refund).
Now the Federal filing has been accepted. Hope there are no more problems.
I'm not a tax expert but this approach worked for me. There was no reason to invoke the form 4972. We did not get a lump sum and both of us are not so old.
