Topic on Talk:Tom Clancy's Splinter Cell: Blacklist
This is a permanent link to the first version of this post.
You can view later versions on the post history page.
@OP Can you try to use a VPN along with your friend? Eventually mobile connection to exclude problem with provider? Probably you also tried to disable firewall, enabling UPNP on router. Generally keeping NAT open/necessary ports open/forwarded only if provider doesn't block it (mobile networks usually do it unfortunately).