The add to cart button in gk4 is not working

in my site technostationus.com
I activated the add to cart button in the mod_show_gk4
and it shows but does nothing when you click on it.
crome's inspector says this is the issue.

Uncaught TypeError: Cannot set property 'value' of undefined k2store.js:210
k2storeAddToCart k2store.js:210
onclick /tienda/:436

firefox says: form.task is undefined. in .....media/k2store/js/k2store.js
same line 210

so whats wrong with it.
the button works in the categories, and i am working with k2store. no items in the virtuemart

Hi

I can see this same question for the 3rd time. Please keep conversation in the one I've answered already. I'm closing this one.