Issue with getting a drop down to pre-populate text fields

Hi

I have a form where I want to populate a couple of fields when an option from a drop down is selected.

My column headers are

Product (This is the dropdown)

Description

Item Code

I found some code on these forums from a similar query and have popped it in but Im not sure if Im doing it right as I am getting errors.

Should I be selecting 'change' under show?

The code I have used is:

var sNewSel = event.value;

     switch (sNewSel) {

       case "Scott Slimroll Hand Towel Roll":

         this.getField("Description").value = "Scott Slimroll Hand Towel Roll - 1ply - White";

         this.getField("ItemCode").value = "PTKCSLHTROL1P-W";

         break;

     case "Scott 36 Folded Toilet Tissue":

         this.getField("Description").value = "Scott 36 Folded Toilet Tissue 36 x 100";

         this.getField("ItemCode").value = "PTKCSCTTIS2P-W";

         break;

     }

I have Commit on Select selected

Whats gone wrong?? The error I get is: