That's what I was thinking too, but for me there are never pop ups, just the inline error messsage, which I get when I press ADD TO CART. So it's in my template, just not coming up when I change the pull down. If you have a minute and wouldn't mind a quick peak the site is here...
http://www.boozingtees.com/product.php?productid=16145
An exception is a Pink Hoodie.
Thanks in advance!!!
James