mrouted doesn't forward packets

Hello,
I have a linux machine that I want to act as multicast router. For it, 
I've installed mrouted but after all configuration and settings, it 
doesn't forward multicast packets. I've checked these kernel and 
mrouted settings and they seem to be right. So what happens? Anybody 
could help me? Maybe there is a "trick" that I'm not be able to see...

Thank you very much in advance
Miriam