Channels have stopped working

[Rosemary4]

My hd channel have stopped working one 2 of my boxes, the main box and one of the multi screen boxes but i have a sky HD subscription 

[Mark39]

What's the error message? What kind of boxes are they - Sky+ or Sky+HD?

[Rosemary4]

Sky+hd boxes and it says to view this channel please upgrade subscription but I have a sky had subscription plus it's only on 2 of the boxes, the other 2 can view the channels