I have a similar problem, only a little stranger. I can play Generals on-line just fine; I can play Zero Hour on-line as well; But when my buddy and I try to play Zero Hour on-line at the same time, we get booted out before we can even build a map. A "Lost Connection" error appears. We have been playing Zero Hour since it came out without any problems, but this issue started around the holidays.
Has anyone had this same issue?