Inside MC preloaders dont work

All the information I’ve seen about preloaders show that one must make the preloader in the main scene, don’t know why, It would be nice someone could explain me…
I’m building www.satorno.com with a fancy preloader, since i tryed making a group mc to contain all the elements of the preloader it stoped working. What i find strange is that sometimes grouping a simple preloader in a mc does work. Where can i find an advanced tutorial of preloaders? :hr: