There are a couple of thing I would do if this was happening on my Slingbox.
First, I would make sure the IR cable(s) are connected to the Slingbox, and positioned in front of the cable box so that the bulbs are pointed towards the front panel of your cable box.
Next, I would want to try reconfiguring my remote control. Here is an article regarding that process:
If you can't find the cable box manufacturer and model number of your cable box, choose the model number that is closest to your cable box.
Let me know if that doesn't work. Hope this helps!