Assign script in selection portal not working.

[Veronica]

I am using 8.5 adv and I am trying to fill a field in my Assignments TO from a related Position TO. I am filtering the portal by programs. I have a dozen programs and almost a thousand positions all total. The filter is working. When I select a program from the filtered global field it enters that program key in the foreign match key of the assignments TO. It also filters the positions for the selected program in the portal of the Position TO. In the portal I have a button with an "Assign" script which is supposed to simply take a value from the selected row and enter it in a foreign match key field in the Assignments TO. But the Assign script is not working. It is:

Set field[Assignments_TO::_kf_Position_Code; Position_TO::_kp_Position_Code]

Is there anything wrong with this?