Try unplugging the CPC card from the network temporarily and then pinging the IP address again. If you still get a reply, you may have an IP conflict somewhere on the network.

Do you have any way to try connecting via serial cable at the site in question? If you can't connect that way either, you may have a bad CPC card. That's a pretty big leap without doing any testing but I've recently had a CPC card with the exact same problem.