G400 UDP Communication on local link using EthernetBuiltIn

I am trying to connect from a computer to a G400 connected directly via an ethernet cable (using EthernetBuiltIn). The G400 will be running as a server, accepting messages from the computer (UDP preferable, possibly using HTTP otherwise). I cannot ping the G400 using the ip address configured using fez config (169.254.x.x, subnet mask set to, getting the message ‘Destination Host Unreachable’. Any suggestions on how I need to configure this?
Window firewall has been turned off during testing, so that is not the issue. I can ping other windows machines no problem using this setup. This is using .net MF 4.3, device firmware version

can i propose a simple alternate test please? Assign a valid IP address and subnet mask to the PC and the G400, and ensure you have a crossover cable (or confirm your computer is fully able to detect that X-over is needed). By doing this you remove auto-config fromt he equation, and then do the tests again

I believe configuring an IP the address with fez config is not enough. you must also initialize in software.

Is this a custom board, or a GHI board?

It is a GHI dev board, not using the custom board yet.
I added code to initialize the EthernetBuiltIn with a static link local ip and I can now succesfully ping (both with standard ethernet and crossover). Thanks for the help guys. Hopefully now the server part will be easy.