Checkout not working

Hi there, I’m really hoping someone can help me!
I’m using Wootheme Shelflife.
On my site (www.hoshhome.co.uk), when clicking ‘place order’ at checkout, I get an error saying ‘Action failed. Please refresh the page and retry’. I’ve changed the theme many times, deactivated all of the plug ins and done other things to try and resolve the issue but I can’t! A couple of weeks ago I was facing the same error in the cart (an error showed when trying to update cart or proceed to checkout), but then I updated Woocommerce and the problem switched to checkout!
It’s very frustrating because until I sort this, I can’t sell anything!
Thanks and eternally grateful 🙂

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