Hi,
There was indeed a mistake in our plugin, thanks to edit the file "\plugins\hikashop\google_products\google_products.xml" and replace the second occurence of:
<param name="identifier_exists" type="text" size="50" default="" label="Identifier exists" description="Tells google if an identifier (brand, gtin, mpn) exists for your products (you can use either 'TURE' or 'FALSE' and no other value is allowed). If you enter here the column name of a custom product field, it will use the value of the custom field for each product allowing you to have a identifiers for some products and not for others." />
By:
<field name="identifier_exists" type="text" size="50" default="" label="Identifier exists" description="Tells google if an identifier (brand, gtin, mpn) exists for your products (you can use either 'TURE' or 'FALSE' and no other value is allowed). If you enter here the column name of a custom product field, it will use the value of the custom field for each product allowing you to have a identifiers for some products and not for others." />