If the Hardware Addr shows as incomplete, it's normally due to a device not reponding. Check to see if the device is up.
When a router receives a packet for a specific ip and the router does not have its MAC address in its arp cache, then the router will arp for the MAC address. The router will then wait for a response. If other packets come into the router destined for that same IP, during that minute, the router will not send out the arp requests, but instead throttle the requests, and the Hardware address will be shown incomplete. Basically the device with this IP is not responding to arp
