This is what I always do:
Go to your DirecTv online account page, find the “Your Equipment” page, then refresh your receivers. Even though one of them is working now, you might as well refresh both while you are doing it. After doing that and waiting about five minutes (it usually only takes a second or two, though), if you still get the 771, push the red reset button on the receiver that isn’t working.
2016 Rockwood Windjammer 3029W Diamond
2015 Chevy 3500HD LTZ 6.0 Crew Cab 4x4 Long Bed 4.10:1 SRW