If there is an amount in box 14 then there has to be an amount in box 16. So if there is an amount in box 14 then enter the amount from box 2 into box 16.
If there is no amount in box 14 then you should just leave boxes 14, 15 and 16 blank. If you entered any information into any of these boxes then you should delete it.
I am getting an error message after entering an amount in Box 14 but no amount in Box 16. There is nothing in Box 16 on Form 1099-R and the amounts in Box 1 and Box 2a are the same. I cannot continue