Maybe a Firewall problem.. Can't remember where I cribbed the following explanation from.. but it might help.
How force IP works in Firewalled
http://www.gnutellaforums.com/showth...5&pagenumber=2
Basically, a firewall blocks network ports for any incoming traffic (and potentially outgoing, but we don't care about that for now). You can customize this behavior, but I'll get to that in a second.
In addition to blocking ports, the firewall also masks your "real" ip address, reporting the ip address of the firewall itself.
The result of this is that no one can initiate any connection to you -- either a Gnutella connection or an HTTP file transfer connection (really any TCP connection at all). The firewalled user has to initiate any connection.
This has several consequences, among them that firewalled hosts end up sapping the connection slots on the network, as they establish connetions with other users, but do not allow others to establish connections with them. The fact that they are firewalled also complicates downloading from firewalled hosts, as the firewalled host also has to initiate the file transfer through a process called a "push request."
So, forcing your ip gets around this. First, you have to open up a port on your firewall, and enter that port in the port field of the force ip screen. Then, you just need to enter your "real" ip address behind the firewall -- the address that your machine reports if you type "ipconfig" on the command line. This is quite beneficial because it allows you the security of a firewall while allowing you to participate on Gnutella as if you weren't, which helps the network out by providing more connection slots and making it easier to upload from you.
I hope that makes some sense.