Problem with Loader object, some users don´t see the content

I´m having a weird problem where a Flash is loading another swf object through the a Loader object. For a certain group of users (in a different location), this swf does not load, and no error message or anything is returned.

For me and others in my office, this works without a hitch. I´ve tried adding various event listeners to the Loader, but it appears that for these people no events are fired. The other content in the main swf works just fine. This does not appear to be caused by firewall/adblockers/popup blockers, etc.

I´m fairly new to Flash development, and I really have no idea where to start debugging this. Anyone ever experienced something like this? The swf that is supposed to be loaded is a loader itself, which again loads another, final swf. Everything is served through a webpage, so it´s really weird to see this inconsistent behaviour.

If anyone can give me some tips on where to start, it would be greatly appreciated.