After the splash screen, I get a message that tells me "Unexpectedly Disconnected from Online Services". Now, I know this can't actually be the case, because I maintain smooth skype calls no problem while it tells me. It also lets me log on initially and choose a persona, so it is at least connecting to something initially.
I've so far fooled around with compatibility mods, running as administrator... I don't have a firewall up or anything like that, and I've checked the hosts file. Haven't done anything as drastic as reinstall windows or C&C 4, yet.
I'm using 64-bit Windows 7, and the threads about so far haven't been helpful.