Notice: Undefined property: stdClass::$unknown in views_handler_field->render()

Hi there,

I recently added Commerce to my test site and am getting this notice after adding a product to the cart.

Notice: Undefined property: stdClass::$unknown in views_handler_field->render() (line 736 of C:\wamp\www\my-site\sites\all\modules\views\handlers\views_handler_field.inc).

The product will only add to the cart if I create a new product display node then, straight away click 'add to cart'. If I navigate away to a different page then go back to the node and click 'add to cart', it doesn't get added or show any error/warning messages (just refreshes the page)...

Also, if I view the cart with a product in it. The price column is empty & the total column is also empty with a header of "Broken handler field_data_commerce_total.commerce_total"

I know it's most likely my error rather than Commerce, but at this point I have no idea what to look for? Appreciate any help that you can give me. Thanks!