Damn, thanks Svper. That's 100% my symptoms and background - I'm on a fresh install of wow, and have not spent a requisite amount of time single-boxing. I did wait for the launcher to hit 100% before I launched any multiboxing, but I guess there's in-game downloading that can't happen correctly while multiboxing.

With any luck, my clearing all cache and spending time doing one-session auction work will rectify the problem.