I've been trying to play the Rush trailer in multiplayer -- I've tried Bnet, LAN, direct connect. For test purposes, I want to play it by myself, but every time I start the game, it says "scenario file still being distributed." Even though it's just me! But it works fine in single-player mode! This has also happened with other maps, both with other people and just by myself... why?!?

When the problem is with starcraft, not specifically 1 map, a reinstall is ALWAYS in order. Considering Starcraft installs in around 5 minutes on any decent computer, and you lose none of your maps, I don't think it's much of a problem. As to your error, I've never encountered it on single player UDP, so I can't help you there. It may have something to do with the title name, but I don't know much about the rush trailer.

As far as I can remember I had the same problem. It's an error of the map, not starcraft. Try changing Map/Force names. If that doesn't help you might want to PM Tuxlar (the Maker) he's also registered here on SEN.

Delete the file and redownload it. Try that.