I too am having this exact same problem with trying to register a lawnmower. This website needs some work. I hope someone at corporate IT is reading this. What would be helpful is to put an EXAMPLE of what is valid to enter in that field. Seriously... how hard can it be?
/images/us/support/product-registration/
The product of my lawn mower (per the big label on the box): 96145000900
The result: "No product found"
I hope the mower works better than this website.