It looks like the network connector, that allows multiplayer games, GPG net has been deactivated. It is not clear, if this is permanent. But in the meanwhile, there is a community based program called forged alliance forever that replaces it and it might even work better than GPG net (which was never of high quality in the first place, GPG did an amazing incredible job in creating a game as amazing and unique among all RTSes as Supreme Commander and Forged alliance (does not apply to SupCom2, as that is a Souped down RTT (real time tactical, as many elements of SupCom 1 got removed), BUT network programming does not seem to be their forte.
SupCom 2 is more "streamlined", i.e. dummed down and the whole amazing thing about SupCom 1 and FA (the standalone extension) was that it required so much brains and is so gigantic. It is the only true RTS, that requires STRATEGY and STRATEGIC THINKING.