The error might be due to the part not making proper contact with the socket, either because it is not properly seated in the socket (a common problem with the larger ceramic packages), the socket leads are bent, or because bits of plating scraped off the device leads have fallen into the socket and are causing shorts.
Inspect the leads on the socket and if any bits of plating are present, tap the socket against a hard surface to shake these out. Check for bent leads in the socket and straighten these out if possible (the socket may need to be replaced). If there is any possibility that the device is not properly seated in the socket, try reseating it in the socket to see if you can get better contact.
There has also been an isolated case of an incorrect algorithm in a 3rd-party programmer that showed this same symptom. Please ensure that you have the vendor's latest algorithm version from their Web site.