Ah, so it works for the full API but not the chooser? or have they fixed the content servers? This is what Dropbox Support originally told me when I contacted them about the problem:
> Thanks for writing in. It looks like the issue here is that our content servers (dl.dropbox.com) don't currently allow arbitrary cross domain access in JavaScript. (This doesn't apply to accessing the file directly in your browser, or downloading to your server locally, which is generally what one would do with the link returned by Chooser.) […] This is something that would need to be enabled on our side, so I'll be sure to pass this on as feedback.