Hi, bjmcadam! Our database shows that serial numbers beginning with KRHR correspond to the PIXMA TS6420a, specifically black units sold in the United States. If you're based in the US and you bought this from a dealer in the US, we recommend double-checking the serial number and trying again. The serial number should consist of the 4 letters followed by 5 numbers (e.g. KRHR12345). If the number doesn't follow that format, your registration won't accept it.
If you continue to have trouble, please give our PIXMA support team a call at 1-800-OK-CANON (1-800-652-2666) and they'll be glad to investigate further. You can reach them Monday through Friday.
Have a great day!
