Recording to dvd from sky + box

Question

Sometimes the dvd recorder will let me record for about 10-15 minutes then goes into pause and the Copywrite Protected message comes up and will not record from that point.........Other times i get that same message from the second i press Record on the dvd recorder remote.........other times it will allow me to record a whole hour or two .......it is very unpredictable.
Any help will be appreciated....Thanks.