I had the same problem. Restoring the default product.tpl file did not work. The solution was to edit the ajax-cart.js as described below.
Edit the ajax-cart.js file ('your theme' > js > modules > blockcart. Around line 141 where it reads for product page 'add' button... comment the if out. The result should look like this:
//for product page 'add' button... // if ($('.cart_block').length) { $(document).off('click', '#add_to_cart button').on('click', '#add_to_cart button', function(e){ e.preventDefault(); ajaxCart.add($('#product_page_product_id').val(), $('#idCombination').val(), true, null, $('#quantity_wanted').val(), null); }); // }
Worked for me.