Check your signal strength. It's possible you may need your dish re-peaked. I'm guessing that a txp hosting the channels has a really low reading (below 70).
I ended up having to re-aim my dish, even after I had another installer come out. I've managed to get 80s-90s on all 103(b) txprs.
I'm having the same problem. NFL Network HD is freezing when it finds the signal it looks like. Sometimes nothing ever shows up. Some of my channels work fine, but the NFL and some others aren't. Its weird because I turned to the test channel on 9300 this morning and they were broadcasting NFL HD fine. I turn to 212 and it can't even come in. Not sure whats up.
I've been having signal problems with 103b for about a week (since they started testing 103b). I called D* today and after much trouble shooting over the phone they are coming out to re-peak my dish on monday.