Most likely, your doing a NAT hide translation with your internal networks (If your like most companies). When your ICQ agent reports back to the client (or server) that you want to start a file transfer, the client with create a NEW and seperate connection to feed the data back through. That means since your NATing, the other person is trying to connect to your firewall's external interface. The firewall has no way to know to connect this particular connection back to you. The solution is to do a static NAT and give the internal machine an external address and allow the ports needed although this is HIGHLY not recomended. If you do choose to allow a 95/98 box connect to the internet that is in your internal network, dont be surprised when its used by a hacker to wreck havoc later.