Most categories require sellers to use a product identifier to create new products on the amazon.com website. The most common identifier is a UPC. If you do not provide a UPC, EAN, ISBN, or ASIN, then you will receive this error message. 

To add a product identifier, you will need to:

• Navigate to Listings-->Queued Listings-->Product Details.
• Add a product identifier in the product details
• Click the blue "Save Button"
• Go back to Queued Listings--> select the product--> click the blue "Submit Revisions"

If you do not have a product identifier, here is how to obtain one; https://www.amazon.com/gp/help/customer/display.html?nodeId=200202190#get_code