It seems to be an issue with the network, it could be at home or remotely.
You need to check that the router is properly setup for Internet Viewing and also that the port forward rule on it doesn't have time limitations. You can get some troubleshooting steps at this link to setup manually the Internet Viewing,
If you are trying to connect to the Slingbox remotely, you can try to a different network and a different computer too, so if the issue persists we can confirm that the issue is at home. Take a look at this link