Windows Server 2008 R2 network adapter stops working, requires hard reboot

From http://linux-ip.net/html/ether-arp.html:

If no ARP cache entry exists for a requested destination IP, the kernel will generate mcast_solicit ARP requests until receiving an answer. During this discovery period, the ARP cache entry will be listed in an incomplete state. If the lookup does not succeed after the specified number of ARP requests, the ARP cache entry will be listed in a failed state. If the lookup does succeed, the kernel enters the response into the ARP cache and resets the confirmation and update timers.

It looks like your gateway box is not responding (or responding too slowly) to ARP requests from your gateway box. Does that <incomplete> eventually switch to <failed>? What network hardware do you have between the the server and the gateway? Is it possible broadcast ARP requests are being filtered or blocked somewhere between the two hosts?

It means that you pinged the address, the IP has a PTR record (hence the name) but nothing responded from the machine in question. When we see this it's most commonly due to a subnet mask being set incorrectly - or in the case of IPs bound to a loopback interface that were accidentally bound to the eth interface instead.

What is 196.220? What is it's relationship with 196.211? I'm assuming that .220 is one of the HA Proxy hosts. When you run ifconfig -a & arp -a on it what does it show?