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http://www.linuxquestions.org/questions/programming-9/%5Bc%5D-raw-socket-set-source-ip-to-0-0-0-0-0-a-712267/
I'm not sure whether it's affecting you, but MS locked the possibility of "forging" packets using Socket API, to prevent kids from writing spoofing tools easily

The move is plainly stupid, because you can still forge packets using lower-level access to the network driver (NDIS - in case of Windows)
Well... that's what NIC is for... creating packets... Don't ask me to explain Microsoft's reasoning....