I had the same error: "Cannot use object of type Product as array".

In Prestashop 1.7: "Objects are no longer passed to Smarty. We only use arrays now." (http://build.prestashop.com/news/module-development-changes-in-17/#general-information)

In my case, it was a module 'productcomments'. He overwrites the "product" index and changes "array" to "object".