Is your HR24-100 set for a RF remote rather than IR? Reading from here:
I'm kind of a geek so I'll be reading some of the technical threads to learn more about the system. My only other wish would be if the IR and RF could receive together. I have a slingbox but like the RF remote for controlling the HR24 in another room. I can't get my slingbox to work since the receiver turns off its IR when using an RF remote. Is there a hack to change that?
So assuming nothing has changed since the above post, if the HR24-100 is set to receive commands from a RF remote the IR "eye" is turned off until the receiver is turned on (typically via the RF remote or front panel).
See the support article My set-top box is not responding to remote commands.