missing cable channels

After probably a month of messing around and changing things. I've finally got a setup how I like with pretty much everything working. The only thing that I can't seem to figure out is.. When I do a scan on the cable tuner I find loads of channels and most work fine. But there are some that when I look at the channel list are greyed out eg. History HD even tho H2 HD works fine. Is there any reason for this and is there a way to fix it?

Any advice appreciated.

Many thanks

Sound like a bit too much trouble to me. Think I can manage with just the standard channel. I have a openbox a few years ago and had to have something connected to the ariel as it didn't pick some of the channels up. Something to do with polarisation or something. Is it something like that?