eBay return this error message when the item you are publishing does not have at least one associated picture in Prestashop.
Therefore make sure that your product has at least one cover photo on the site and try again.
This error can also occur with multi-variations products, when you have linked all your pictures to variations (including the cover). You can overcome this , by enabling the option “Send cover picture to eBay even if linked as a variation” in General tab of the module.