1099-R form with a blank for State distribution

Anything in box 14? If not then leave boxes 14, 15 & 16 blank, no spaces. If you have withholding in box 14 then enter the same amount as in box 2a. If box 2a is blank use the amount from box 1.

Box 14 is not blank. Box 2a has an amount that is different that Box 14.

I attempted to make the changes you suggested and still receive the same result - Answers to review still needs review.

Box14 shows amount of State Tax withheld. Box 2a shows the taxable amount of distribution reported in box 1. 

Enter the amount from Box 2a in box 16 for state distribution. 

That worked, thank you.

I wonder if the fact that my entry into Turbo Tax is different than the form provided to me, however.

It will not cause any problems for you to enter the Box 1 amount in Box 16.  Many form providers don't fill this box for many reasons. Filling it in tells the program how to allocate the money on your state return.