I found my answer on this forum:
"From: bthatcher2005Jun 8, 2011 2:13 PM in response to: quita
In fact the solution is that Slingbox programmers missed a step. If none of the options to connect to work (they don't when you are connected direct to a TV antenna cable) just ignore that page and continue. The next page gives you the option of connecting to either a digital TV antenna or an analogue one, and then Slingbox scans all available frequencies just like a regular TV or DVR. Job done, and my slingbox works fine. Good luck. Bill"The problem is definitely a coding problem. Disconnect all other sources before trying to setup the Coaxial antenna inputs. When it scans all inputs and finds no signal at all, it will then allow you to scan for cable or antenna channels. Then, once your are done setting up your cable input, you can reconnect your other inputs (Svideo, Composite, Component).Good luck!
I want to thank you for pointing me toward the solution to this problem of not being able to configure a coax input source in my SB Pro HD after having already configured an S-Video input source. In my case, just disconnecting all of the cables before configuring the coax did not solve the problem, BUT disconnecting all of the cables and doing a hard reset on the SB; then FIRST configuring the coax input source, and then SECOND, adding the other S-Video input source did the trick for me, and now I am a happy camper with the ability to sling two different video inputs (although not both simultaneously of course).