What I could gather from solutions to similar problems posted elsewhere is this-
It's a non-problem. What happens is the IP address's LEASE expired. If the machine is off, the lease expires and some other machine asks for an IP, then it can get the now free IP. When the box that had the IP comes back, a bug in the DHCP code by you-know-who fails to release the old IP and to get a new one. The error message occurs and you get to learn about IP leases.
You can't fix this one, but can release and renew to get a new IP.
So, I guess Microsoft is to blame
