I'm not familiar with Sky TV's services, don't have TV myself, but wanted to pass on a query from a friend. They spend a few months out of the country so don't always have Sky hooked up. When firing it up again, they got the usual multitude of channels but then after a little while could only get channels 1,2,3 plus RadioNZ/Concert I think. Would that mean the subscription has expired? Or would it be some sort of OTA update of some sort?
If they have their decoder off for long enough, they can miss the EMM's issued via Satellite that keeps their smart card up to date and valid.
Leaving the decoder on for a good length of time (not sure exactly how long it is between EMM's - but could be anywhere from 1 to lots of days - someone else will know more about this than me) will hopefully get them working again, but if it has been long enough, they'll need to contact SKY and get them to re-send an update (the CSR can do this - just explain to them that the decoder has been off for X months, and the non-FTA channels are no longer working).
Happy to be corrected by the more knowledgeable folk!