You are entering the form in the wrong place or checked the wrong type of form. An RRB-1099 is entered under social security. An RRB-1099-R is entered under the Pensions, IRAs topic.
If you have an RRB-1099-R and are correctly trying to enter it under Pensions, then you must have chosen the wrong type of 1099-R on the very first screen when you start that interview. Use the Back button to select the correct type of 1099-R.
If you are trying to enter an RRB-1099 under Pensions instead of Social Security, you'll have to delete what you have entered there and go to the Social Security topic instead.
