I have not tried it, but it is true sorta. You can load external content and swfs from the same domain, but pulling it from another site can cause problems. However if a site is offering it out like that it could, it depends on if the site has a crossdomain.xml policy file. It gets complicated, but box.net has one it appears.
The only thing I can think of besides logical coding errors is that when you embed it like that in Flash, it doesn't like the query strings at the end (?...stuff). Try it without, and double check the code is doing what you think, or post it all here again with changes.