do you have your old v box remote? Is your setup all the same manufacture/models? Should not be a problem but I was wonder if you were using a receiver which did not have a IR extenders function. Make sure that there is nothing in the way of the receiver/remote (eg. don't just point it at the telly) if the receiver is placed at the back of the telly.
I've bought one of these
http://www.maplin.co.uk/module.aspx?...117415&doy=5m9 so I could put my v+box and transmitter in a cabient downstairs. It works brilliantly. I can change channel anywhere in the house with this bit of kit. Still dont know how it works. but its a picks up the Ifrared signal then changes it to RF signal. I dont know how it knows what you pressed as it is little battery that fits into the existing V+ or any other remote then a receiver sticks onto the front of the v+box,