Thank you for participating in the Slingbox Answers Forum. In regards to the message you are receiving, if you have updated and added certain things to the setup you had, it could be a firewall within the router itself. Router's will update, and sometimes during that update the firewall is enabled. If it seemed to be working fine since the changes were made, I would recommend contacting your router manufacturer and also checking your firewalls on the PC itself.
Hope this Helps. If you do have further questions feel free to contact us via our phone support at 877-467-5464.
The Sling Moderation Team.