@152718rag
For a few states, like NY...it won't let you move on unless the is a $$ amount in box 16 of the 1099-R...even if it is empty on your actual 1099-R.
SO, if there is an actual $$ amount in box 2a (not zero, nor empty), enter that $$ amount in box 16.
If box 2a is empty/undetermined, then you use the Federally-taxable amount of box 1...which is usually just box 1.....into box 16 as the state distribution amount.