Since you cannot connect to the Slingbox remotely, it's necessary to determine if the issue is with the Slingbox itself or the Internet Viewing settings on the router. I recommend to confirm with your friend if he is able to connect to the Slingbox locally (same network where the Slingbox is). If the issue is only remotely, it will be necessary to run locally the Internet Viewing setup using Setup at slingbox.com. Have a look at this link,
Let us know how it works.