I assume you have already done a proper Forum Search for your model number in case other people have already answered your question ?
If so and that didn't help then check out this thread: https://community.sling.com/message/10363#10363
Come back if it that doesn't help either.
I have the same problem. That thread didn't help. I'm stuck on CBS. When I change the channel.. it acts like it wants to change.. then it stays. The information goes to the new channel but the video is still CBS. I've reset the source, the iPad, uninstalled the app and installed it again, and, of course, reset the sling box.
Surprised my post didn't help as it details your problem quite comprehensively. For some reason the IR signal being transmitted is either not reaching the cable/satellite box or it is the wrong code. So to repeat some of the recommendations that were covered in that post:
1. Does it work on a PC ? (You need to decide if the iPad app is at fault or the Slingbox)
2. By 'reset' the source I assume you mean you have rerun the Reconfigure Inputs routine ?
3. Have you used the external IR Blaster ?
4. Have you checked the IR is actually firing ?