Can't Use Option on mystore theme

I'm using the mystore theme and it works fine except that when I add an option (i.e. color etc.) and then try to apply the option to a sale, when I press "Add to Cart", nothing happens. It doesn't add it to the cart, the page just resets.

Can anyone assist me with this as the Author has not responded after several emails, so I have no hope that they will.

Thank you,

SN