TurboTax asks these questions if you told TurboTax to use the Simplified Method to calculate a taxable amount different than the taxable amount reported in box 2a of the Form 1099-R.  If you made no after-tax investment in the pension plan or the amount shown in box 2a is correct, you should not be using the Simplified Method to calculate a different taxable amount.  You might need to delete and reenter the Form 1099-R.

Box 2a is blank ant the box for "taxable amount not determined" is marked.  

In that case:

If you made no after-tax investment in the plan, the entire distribution is taxable and you should not be using the Simplified Method.

If you made an after-tax investment in the plan, you need to use the Simplified Method to calculate the taxable amount unless you've already recovered all of your investment in the plan through past pension payments.