Do you use IPv6 in your network? This may just be warnings really, Win7 saying it can't get IPv6 address from the DHCP server.
I've disabled IPv6 on the WiFi interface. Still there is the same problem:
C:\Windows\system32>ipconfig /renew WiFi
Windows IP Configuration
An error occurred while renewing interface WiFi : unable to contact your DHCP server. Request has timed out.
In the DHCP log of monowall, there is nothing logged about these attempts. To reiterate, the lease was obtained ok, but the renewal attempts fail. Anyone else seeing this?