Hi,
In the HikaShop configuration, and in each product edit form and in each category edit form, you can find a setting called "Layout on product page".
This error indicates that you must have selected a particular layout file which you then deleted and thus the system cannot find it anymore when trying to display the product details pages with that layout.
So you need to check that setting (probably the one in the HikaShop configuration, to set it to "default" and then save the configuration once. That should make these pages work again.