As I understand it, client tools like Silverlight (and possibly Flash / Javascript) cause a cross-domain error when you try to connect to a server, which is usually only allowed when it is created for the same domain to which it was sent Page (some origin policy).
A cross-domain error can occur, for example, when you view a page on your test server, when it tries to call your live server, or when you view a test page as a local file using the file: // protocol.
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