getURL with loaded external swfs

Hi All.

I have a swf (a.swf), which loads another swf (b.swf) into it.

b.swf then has a getURL call in it.

on (release) {
getURL ("http://www.google.com/", "_blank");
}

a.swf is being viewed in a webpage, and will only ever be run locally.
I’ve tested this on Chrome, Firefox and Safari. No dice

Everything tells me this should work. But it doesn’t.
I’m really stuck and this is driving me bananas

Thanks
Alex