I'm having a similar problem. I installed Service Pack 2 so I'd be on the same page as everyone else, even though ive been reading about it conflicting with shareaza. But it gave me a new insight into the problem: Every other internet program i run, Windows firewall asks me if I want to block it or not. But not for shareaza. So apparently it isn't even getting as far as my computer's own internal security, let alone my router or my ISP. It should also be noted that I have no problem sending or receiving data through any other applications. So I really doubt it has anything whatsoever to do with my router, my ISP, or even windows security.