Millisecond Forums

Hi, I have a slider element which looks something like this:
<slider Q3>
/ caption = "sometext."
/ labels = ("Extremely likely", "Likely", "Somewhat likely", "Neither likely nor unlikely", "Somewhat unlikely", "Unlikely", "Extremely likely")
/ range = (1, 7)
/ size = (90%, 5%)
/ slidersize = (90%, 5%)
/ position = (5%, 75%)
/ required = true
</slider>

However, whenever I try to add a line to accept only left mouse clicks as valid responses -- 
/ validresponse = (lbuttondown)
Inquisit shows an error message saying that "'lbuttondown' Expression contains an unknown element or property name."

I'm not sure where I'm going wrong. My main goal is to ensure that participants can only click on slider responses, not input their answers using mouse scroll.

TIA for your advice!