I can't start any new campaigns since 1.5

I just installed 1.5 and I had a small bout of multiplayer, then, I decided to start a new campaign. I clicked on "Imperial Campaign", and picked a faction, but when I start, it refers me back to the Single Player page. I've done this many times, even with the Prolouge campaign. Saved games and custom battles work, but no new campaigns work.

I'm willing to go back to 1.3 and do a fresh re-install, but that means I can't play multiplayer anymore.

Any help? I haven't installed any new mods, nor have I messed with any game files.