Variable Products Not Adding to Cart

Hi

I am unable to add variable products to my cart having updated to WP3.9

I select the options and “add to cart” but nothing is added

This does not happen on standard products

I have:
Deactivated all plugins
Switched to standard theme
Cleared cache
Looked in the console for JS errors – seems to be ok
Checked WC settings and all ok

Using WC 2.1.7

Any help gratefully received

Link