setFocus not working

I have a 'total' field on a purchase order form, am using below custom validation script to ensure the value does not exceed 7500.00.  That part works ok, it gives the error message ok, but I'm trying to get the cursor to go back to the top of the Quantity column (QTY.0), but it doesn't seem to be doing that.  As it is, it throws the cursor to the bottom of the page where the 'total' field is. What am I missing?  Thank you!

if((event.value <= 7500.00)){//Valid}else{
app.alert("ERROR: Total exceeds Site PO Limit. Please revise price or quantity.", 3);
event.rc = false; 
this.getField("QTY.0").setFocus();}