Thanks for posting in the forums! I apologize for the inconvenience of not being able to connect to your Slingbox. I'm sorry for the delayed response. It sound like there is a firewall or security program on the PC that is not allowing you to connect.
Do you have any form of an antivirus software on the PC, at all. If so, that is most likely what is causing the issue.
Below is a link to an article that explains this in greater detail:
Hope this helps!
The Sling Moderation Team