Your 1099-R should have a Box 16 - are you sure you have a 1099-R. It is usually the amount in box 1 of your 1099-R or it may be $0 if you reside in a state with no income tax. If it is blank, leave it blank.
But if you leave it blank it it high lighted and says there must be a amout in box 16
Yeah, it annoys many folks that a 1099-R is only rarely filled in on a 1099-R form that you receive form the provider....that is very common. I've been receiving 3 different 1099-R forms for many years, and box 16 is never filled in on the forms I receive.
I am somewhat uncertain why, but I think they don't because some states may use the box 1 amount as the state distribution, and some states may use the box 2a value as the state distribution.
For instance, on one of my 1099-R forms, my box 2a value is a couple hundred lower than box 1, due to some after-tax contributions to my traditional 401k. For my state (NC) I must use the box 2a value as the NC state distribution to be entered into box 16.