Script format

I'm trying to create a simple script in which the selectged results in a drop-down menu field causes a specific response in another corresponding field.  The "Property" field is a drop-down menu, and the "AccountingCode" field is where I want the specific result to display.  The below script is what I entered in the AccountingCode field, but doesn't produce any result:

var Property = this.getField("Property").value;
if (Property=="property loss/damage") event.value = APC9AA6;
else if (Property=="real property loss/damage") event.value = APC9BB6;
else event.value = "";

Also, the Property drop-down field contains a blank entry (ie. 10 spaces using the space bar) to create a blank listing as the first entry on the default drop down listing. The purpose is to have the Property field default to blank to cause the employee to make a selection, rather than accidently tabbing through and using one of the pre-listed listings, which if blank, should reflect a blank in the AccountingCode field as well.

Any advice to assist this novice would be greatly appreciated.