DuaneMIS on "[Plugin: YAK for WordPress] YAK For Wordpress CheckOut Error"

I have a product in a post. When I click BUY NOW it is added to my cart.
Post I am buying from is here:
http://pplac.org/2012/12/12/professional-photographer/?preview=true&preview_id=908&preview_nonce=871e46d77a

I created a link to go to the cart at the bottom of the above page, the page 'CART' is the default page created at time of YAK install.
When the page opens I get the following error:

Checkout

Fatal error: main() [<a href='function.main'>function.main</a>]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition &quot;YakItem&quot; of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in /home/content/57/9294457/html/wp-content/plugins/yak-for-wordpress/yak-view-cart.php on line 81
Item	Price	Qty	Subtotal	Remove

Thank You in advance

http://wordpress.org/extend/plugins/yak-for-wordpress/