subproducts - not adding the right item to cart

I've left the problem live at:
http://www.vibecomputing.com/wacom/bamboo

Using the subproducts menu at the bottom, it doesn't add the selected item to the cart. It always adds the same (wrong) item to the cart.

It also shows this error:
warning: implode(): Bad arguments. in /var/www/vhosts/vibecomputing.com/httpdocs/sites/default/modules/ec_live_subproducts/ec_live_subproducts.module on line 1042.
warning: implode(): Bad arguments. in /var/www/vhosts/vibecomputing.com/httpdocs/sites/default/modules/ec_live_subproducts/ec_live_subproducts.module on line 1042.

Any idea of a solution?