As far as I know if your V6 box has been updated and is running 360 software you can only have one remote paired to it, have you tried repairing your remote ?
Here is a link with instructions if you need them,
https://www.virginmedia.com/help/virgin-tv-pairing-tv-remote
Also have you checked the batteries, always a good place to start.
May be worth doing a search on here for Harmony remote, I have seen other posts about Harmony remotes as I don't have one I can't really help any more than that.