What this sound like the Internet Viewing was not setup correctly through the home router. What needs to been done is to go into the home router and port forward for the IP address of the Slingbox to port 5001.
If you do not know how to do this, give Sling Media Technicial Support a call at (020) 7294 0157 for UK support and inform them that you need to get the Slingbox to pass TCP (Transmission Control Protocol) and they will be able to help out.
Keep in mind this has to be done at the location of the Slingbox.
Hope this helps!!!
Sling Media Moderation Team