I am having problem with product variable add to cart not working

We are having problems in variables Some time add to cart button shows up and some time it does not. How to solve this We are bangning our head. Some time it worked in mozilla for chrome it is not working at all
and some time in mozilla it also did not

http://wordpress.org/plugins/woocommerce/

[No bumping. If it’s that urgent after waiting just 20 minutes, consider hiring someone.]