First of all you should realize that it's the *sender* that needs to forward ports on their router, because the receiver is the one making the outgoing connection.. Routers pretty much never block outgoing connections (unless you're connected to some school/office/highly secured network), so it's rarely the receiver's fault.
When your friend sends you a file, you connect to them, meaning if anything is blocking the connection it's his router, not yours. You shouldn't have to fiddle with anything on your end.
Can he dcc send to anybody else? Has his local ip changed recently? If he's on DHCP this is highly possible. This would affect port forwarding. I'll bet good money that something did in fact change in his network that broke his port forwarding configuration.
