I did a general search of the forums and some other web sites, and this quest has previously been bugged in the past; supposedly this was fixed in September.
Previously, it was impossible to get past the inner door using the horn... Well, yes indeed, that is fixed.
However, now once you get in, nothing happens. Whatever trigger mechanism is supposed to start the gathering of bones doesn't fire.
Well, the graphics are nice...
Side note: Other problem getting inside; the mobs are respawning so fast on the outside that the ones you just killed have respawned before you can finish killing the next bunch. Makes it a little tricky...