Hi,
The link
www.zynopets.nl/index.php/Product/107-garvo-knaagdiermix-5540
can only be valid if the homepage of your website is of one of the HikaShop menu item types.
If you have such link after changing that menu item type, it means that you have that URL as canonical URL of your product and that you turned on the "force canonical URLs on listings" setting of the HikaShop configuration.
You'll have to empty the canonical URL of the product so that the system doesn't try to use an invalid link and instead generate itself a new valid link.