Sorry for resurrecting an old thread, but I've just hit the same problem and the forum search led me here.
I am a bit worried that the instructions explain how to change the code on the HDR, but it is not clear to me how the code on its remote handset is changed to match it. Does this happen automatically at the same time as the HDR code changes?
Sorry if this is blindingly obvious, but I didn't want to get stuck with an HDR with a new code that could not then be accessed by either of the remotes.
Thanks for your patience
Keith