The following link will provide you with the explanation about this issue.
Make sure to follow the recommendations and let us know how it works for you.
Like many people who have TV's with cable or sat' boxes, I wish to use the HDMI connections.
The problem is that the Slingbox's only have component and composite inputs.
My cable box (Virgin Media) has HDMI, composite and component outputs, but using the HDMI output from the cable box results in the other outputs being stopped/unavailable.
My solution was to purchase a HDMI splitter box, one input - two output, one output to TV, leaving the other HDMI to connect to a HDMI component converter.
I purchased a HDFury 3 box.
All works well.
For obvious reasons I think, copyright etc, neither Slingbox or Virgin Media support would not tell me of the solution.