See the media section. Please try uploading stuff. It doesn't matter what. I think this update is going to be pretty buggy, so the first person to find an error (and post the complete error text) gets a cookie!
Also make sure to try adding files to a sumbission which you have already submitted. The rule is, if it's your submission you can add new files to it, but you can't remove the existing ones unless you have moderator rights.
BTW, you may need to hit refresh to get the latest stylesheet. Just press F5 right now and get it over with.
Reminder: I had to reset the file manager, so everyone's avatars have to be re-uploaded.