I echo what Scooby just said. I find that this is a major problem with the STBs. A simple reboot does (in my case) provide a solution.
I understand how irritating it can be when this happens - attempting to find a TV Guide or even going out and buying one!! Thought the days of buying a TV guide were behind us.
It has come to my attention that ntl: are in fact looking into this problem to see if they can pinpoint a probable cause for the fault. How long this will take is anyones guess and quite frankly, as patient as I am, I think they will tell us that we are "flicking" through the channels too much or something to that effect.
James