I'm not Angie, obviously, but I do live in LA and have been to a few industry events and parties lately, and I am always amazed at how casual people dress, on the one hand, and how anything goes, on the other hand. It's so frustrating to try to figure out the dress code out here, because celebs wear anything and everything, but the rest of us usually don't have that kind of budget. Even at a premiere there will be some dressed in jeans (albeit $250 jeans) and some dressed in fancy dressy clothes. People don't really expect us mortals to be dressed as nicely as the celebs, so you shouldn't worry too much about that.
If you are representing an organization and want to be on the safe side, you could always wear dressy black pants with a great top and/or jacket, some great accessories and/or some color somewhere in the outfit, or something sparkly. A nice party dress (not a casual day dress) would work too, if that's your style.
I always feel that even my nicest darkest jeans are too casual, but then I always see people in jeans at these things, so I guess it really depends on your age and maybe on your own personal style and what you're comfortable wearing. I wouldn't think you have to wear a gown, but I'm sure there will probably be some people in gowns! I would say wear what you would wear to a really nice fancy party and you should be fine. Make sure you're comfortable and feel like "you," but a fancy party "you." Of course, I could be totally wrong about all of this, too!
