Those are the Voom ch's and they use SDV (Switched Digital Video).
Basically it's ch on demand, and if too many people in your area are tuned into a ch it is unavaible. I had this problem months ago, and had to call many times to get my "node' upgraded to handle more requests. I no longer get this but many people like yourself still do. If you need more info google SDV and Cablevision.