You are correct. There is no 12a on Form 1099-R. It is most likely a type-o.
Generally, the program carries the information to your state for you. Box 14 is the state distribution. If box 12 is blank, do nothing. If you have a box 12 amount, you can fill in the taxable state amount for box 14. Be sure you have a state ID for box 13, and box 12 should be unchecked.
Please delete the form and re-enter the information paying careful attention to the box entries in TurboTax. The simplest remedy is often to delete and re-enter.
