uh ... saying youtube campaign missions is the same as playing them, is like saying watching a war movie is the same as enlisting into the army and serving active duty.

i actually get that problem occasionally too where i'll be unable to download maps, can't create custom games, can't do anything. basically i'll reset my entire internet connection (to get a new streamyx ip cos different gateways perform differently), restart pc, etc, and it works.

[edit] dunno if it's the cause, but also make sure that your windows firewall is unblocked for sc2.

Did u download the blizzard folder they are sharing ? It works 100% for me as my problem is the same as urs..