Average Grade not populating
I'm new to Filemaker and using Pro Adv. I have a layout with a number of portals containing information on a person. I'd like to calculate the Average Grade for that person based on the information shown in the portal. I can't get my script to work. It's returning an error - the operation could not be completed because this layout cannot display the result.
I've also attached a copy of the script in case I've done something wrong.
Any help appreciated.