I have found the problem. I had installed VMware ESXi 4.0 on a server that had been used in a different capacity. The physical server previously had a Windows OS installed which is temporarily running as a virtualized server from a disk image created of the server, now running on a separate disaster recovery server.
The reason the pings are successful to begin with and then fail completely is due to the fact that the virtualized server retained its' old MAC address which is now also being used by the VMWare ESXi 4.0 server. So we had ARP poisoning going on and the VMWare server became unavailable. I shut down the virtualized server and now can ping the VMWare server consistently.
Hope this makes someone else smile!
PS - I had already checked the ESX.cfg, hosts, etc. files and they confirmed the MAC address and IP address as being correct. The problem was that the old server that was running virtualized from a disk image was also using the same MAC address, so when the VMWare server would first appear on the network you could communicate with it but eventually the switch would shut it down and only allow traffic to the virtualized server using that same MAC address (which in this case was a good thing).
Rick
