Select or Deselect a Field Weh the Field is Updated

Select or Deselect a Field Weh the Field is Updated

I have a checkbox field called "Invoiced1". I have the following code in the Field Action, On Load section for a field called "Carrier":
  1. Invoiced1.deselect("Freight");
It works great!

When I try to copy and use the same simple code into the Field Action, On Update, it fails. Saying error on line 0. 
Any ideas? Help is much appreciated. Thanks!