Box 16, State distribution, is the amount of the Gross distribution (Box 1).
This worked for me.
Despite my W-2 not having any info on this box, I entered it into Turbo Tax and was able to continue to file.
I don't mean to take credit for this answer. The answer came from the expert on the first page of this thread.
Sorry, can't remember the name, but thank you for the help.
