I think I may have a similar problem as you here.

I have a few loadClips (MovieClipLoaders) followed immediately by a
loadSound("http://....myfile.mp3",true); call and for some reason the
loadSound() simply doesn't even execute if I use an HTTP file path. I know it
doesn't execute because if I put in a bogus HTTP path, it doesn't even squawk
at me saying "Error loading file...".

If I use a local path to an mp3 on my C:\ drive it works - but I just can't
get it to work with an HTTP url when it comes after those loadClips.

Very strange! and extremely frustrating...!!!! I am finding zero help on the
web on this as well...

Did you every come to any conclusions/discoveries?