It sounds like the IR signal is not able to reach the cable box, or perhaps the Slingbox is configured for the wrong remote. I would recommend checking the placement of the IR sensors, and also try reconfiguring the remote to the proper cable box. If, after checking these articles below, the remote still does not work I would advise requesting for the manufacturer and model on our forums.
Below there are two articles with troubleshooting, and a link that directs you to the forum page to request a .bin file for your cable box.
- IR Emitter/Remote Control Troubleshooting for Slingbox 350 and Slingbox 500
- I got a new cable or satellite set-top box and now I can't control my TV
- Remote Controls Requests
Sling Media Moderation Team