Funny, I had the same thing happen...my oldest dog's chip stopped scanning recently (she's almost 13 and was chipped when she was about 2). We opted against re-chipping her though; she's an old lady who never leaves home and nobody is going to steal a giant, elderly, half-blind mutt. My two younger dogs are much smaller (and are also rescued mutts) and their chips are working fine. They were all chipped by Home Again.