I am doing some testing with Silverlight (I know right!) and I kept getting error #2207 without really getting a detailed description. Well the issue -in MY case- was hat i was trying to download a file cross-domains, and with most plugins it was a no-no. So I just needed to change the source to local file.

[js]
Good:
downloader.open(“GET”, “image-4.jpg”);
Bad
downloader.open(“GET”, “http://www.helmutgranda.com/images/image-4.jpg”);
[/js]