When I first got my 1TB Tivo box, October 2014, I am pretty sure I was able to record 4 programmes at once. All 4 of the red lights on the front would light up. Now if I record 3 programmes, with 3 out of the 4 lights illuminated, and I then try and watch a 4th channel the Tivo returns an error message saying there is only 3 tuners and one of my recordings will stop. What has happened have I been downgraded somehow? My subscription is unchanged.