This site loads fine in Firefox, but in WebKit browsers (Safari and Google Chrome) it won't load the frame, and in Opera I get this error: "The Web site does not permit its content to be displayed in a frame. It must be displayed in a separate window.". I don't expect to be able to actually fix this, as I don't have control over the frames page (only the content of the frame), but my question is: why?

The content of the frame loads fine by itself, and saving the frames page and changing the src of the frame to http://w3.org/ loads fine. I did a bit of searching based on the Opera error, and it seemed to suggest it had to do with redirecting. That URL does indeed redirect, but if I change it to http://mini.milli.no/tonje/main (which doesn't redirect), it still doesn't work. Even Apache directory listings don't work - which to me suggests it's server related. But how can a server do that?

To be total clear, I'm using Mac OS X 10.6.3, and I tested with Safari 4.0.5, Chrome 5.0.375.55, Opera 10.53, and Firefox 3.6.3. Basically, the newest of all of those things currently.