404. That’s an error.

The requested URL /catalog/product_compare/add/product/4313/uenc/aHR0cHM6Ly9zaW1wbGEuYXo6ODA4MC9ldi1oZXl2YW5sYXJpL2F2dG9tb2JpbGUtcXVsbHVxLmh0bWw,/form_key/aeJ60iaD0o94ke8D/ was not found on this server. That’s all we know.