The PIX has an IP address assigned to one of its interfaces that is in use by another device.
It is possible that the PIX was set up with an IP address already in use on the local network. Check this by disconnecting the PIX and pinging the addresses you used for the PIX. You should not get a response since the PIX is out of the network.
Also, check the Address Resolution Protocol (ARP) table on the client and verify the MAC address associated with the PIX's IP address.