A critical error has occurred on this site.

Hi,

I am using the WCK for about a year and a half and it works great. Though since yesterday for some reason, doesn’t work. Usually the price is calculated instantly–now the price does not show. If I click on “add to cart” I receive a message “A critical error has occurred on this site.” How can I fix this issue? Thankful for a fast reply since the shop is live and customers cannot order :-/

The page I need help with: [log in to see the link]