Which is the right serial number? In About Tablet/ status/ serial number it shows as a seven digits and a letter. But on the label on the box this number is listed as CSSN, but there is also a SSN number (letter, two digits,three letters, six digits) which is more "in keeping" with ASUS' way. I went on the ASUS website to register the device but neither number is recognized. I also, more importantly need the correct number for insurance purposes. Any ideas?