I've had this receiver for a number of years (Sony STR-DE635) and it works perfectly for what I have at the moment. But a few weeks ago whenever I change the input to DVD, it will say DVD on the readout on the receiver then 2 seconds later will say "Unlock". I cannot find any information regarding this. I just switched to a different input for my DVD player, but it just really bugs me that I can't figure this out. Any help would be greatly appreciated. Thanks.