overriding locateChild

I've solved the question asked last week using chidlFactory; i've also
tried to use locateChild, but each time I tried (in a LivePage) others
things stopped to work (LivePage makes lots of ajax/comet calls via
XMLHTTPRequest and that urls requested seems not to be handled
propitiated).

Are there something I should have in mind when overriding the method
in this particular class?

On the other hand, I've notice the "Sorry, but I couldn't find the
object you requested." message when I ask (via url) for a page that's
not in the hierarchy. Is this a 404 error message? How do I override
it? How do I raise a 404 error from the code?

Thanks!

-- 
Juanjo Conti